LIBRARY 

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BOILERS 


THE   POWER   HANDBOOKS 

The  best  library  for  the  engineer  and  the  man  who  hopes 
to  be  one. 

This  book  is  one  of  them.  They  are  all  good  —  and 
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BY    PROF.    AUGUSTUS    H.    GILL 

OF  THE  MASSACHUSETTS  INSTITUTE  OF   TECHNOLOGY 

ENGINE  ROOM  CHEMISTRY 

BY  HUBERT   E.   COLLINS 

BOILERS  KNOCKS  AND  KINKS 

SHAFT  GOVERNORS  PUMPS 

ERECTING  WORK  SHAFTING,    PULLEYS     AND 
PIPES  AND  PIPING  BELTING 

BY  F.  E.   MATTHEWS 
REFRIGERATION.     (In  Preparation.) 


HILL   PUBLISHING   COMPANY 

505  PEARL  STREET,   NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 


THE    POWER    HANDBOOKS 


BOILERS 


COMPILED  AND  WRITTEN 
BY 

HUBERT    E.    COLLINS 


OF  TM.; 

'  Of 


1908 

HILL    PUBLISHING    COMPANY 
505  PEARL   STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.G. 

American  Machinist  —  Power  —  The  Engineering  and  Mining  Journal 


Copyright,  1908,  BY  THE    HILL    PUBLISHING    COMPANY 


All  rights  reserved 


Hill  Publishing  Company,  New  York,  U.S.A. 


INTRODUCTION 

THIS  volume  endeavors  to  furnish  the  reader  with 
much  new  and  valuable  material  on  an  old  subject, 
together  with  much  standard  information  which  every 
engineer  likes  to  have  at  his  hand.  A  glance  at  the 
chapter  headings  will  show  the  scope  of  the  book. 
It  will  be  seen  that  the  subject  is  pretty  fully  covered 
from  the  working  conditions  inside  of  a  boiler  to  simple 
talks  on  the  various  phases  of  boiler  practice.  It 
also  covers  the  design  of  boiler  furnaces  for  wood  burn- 
ing, and  much  other  useful  material. 

One  very  important  feature  is  the  portion  on  the 
safety  valve  based  on  Mr.  Fred  R.  Low's  supplement 
to  Power  on  that  subject.  The  author  is  indebted  to 
Mr.  Low  for  permission  to  incorporate  this  material 
in  the  book,  and  to  various  other  contributors,  whose 
articles  have  been  used  as  a  whole  or  in  part  in  the 

work.  ^    ^ 

HUBERT  E.  COLLINS. 

NEW  YORK,  November ;  1908. 


196487 


CONTENTS 

CHAP.  PAGE 

I    WATCHING  A  BOILER  AT  WORK i 

II    SIMPLE  TALK  ON  EFFICIENCY  OF  RIVETED   JOINTS  n 

III  SIMPLE   TALK   ON   THE    BURSTING    STRENGTH   OF 

BOILERS 17 

IV  SIMPLE  TALK  ON  THE    BURSTING    STRENGTH    OF 

BOILERS 24 

V    SIMPLE  TALK  ON  THE  BRACING  OF  HORIZONTAL  RE- 
TURN TUBULAR  BOILERS 30 

VI     CALCULATING  THE  STRENGTH  OF  RIVETED  JOINTS  .  40 
VII     To  FIND  THE  AREA  TO  BE  BRACED  IN  THE  HEADS  OF 

HORIZONTAL  TUBULAR  BOILERS 67 

VIII     GRAPHICAL  DETERMINATION  OF  BOILER  DIMENSIONS  70 

IX    THE  SAFETY  VALVE 75 

X     HORSE-POWER  OF  BOILERS 120 

XI    BOILER  APPLIANCES  AND  THEIR  INSTALLATION      .  123 

XII    CARE  OF  THE  HORIZONTAL  TUBULAR  BOILER  .      .  133 

XIII  CARE  AND  MANAGEMENT  OF  BOILERS     ....  145 

XIV  SETTING  RETURN  TUBULAR  BOILERS        ....  150 
XV     RENEWING  TUBES  IN  A  TUBULAR  BOILER    ...      .  156 

XVI     USE  OF  W'OOD  AS  FUEL  FOR  STEAM  BOILERS  .      .      .  161 

XVII     BOILER  RULES 179 

XVIII     MECHANICAL  TUBE  CLEANERS 184 


vii 


WATCHING  A   BOILER  AT  WORK1 

IF  we  take  a  test-tube  filled  with  water  nearly  to 
the  top  and  hold  it  over  a  Bunsen  flame,  the  water 
boils  violently  and  overflows  the  tube.  This  violent 
over-boiling  is  due  to  the  conflicting  action  of  the 
ascending  and  descending  currents  of  steam  and  water 
in  the  tube.  On  the  other  hand,  if  we  take  a  tube 
shaped  like  a  U,  the  arms  of  which  are  connected 
together  at  the  top,  fill  it  with  water^and  place  one  leg 
of  the  U  in  the  flame,  a  direct  circulation  soon  com- 
mences. The  water  passes  along  in  one  direction  and 
the  steam  is  liberated  at  the  surface.  In  this  case 
there  is  very  little  violent  ebullition,  because  there 
are  no  counter  currents  and  the  steam  is  discharged 
quietly  over  a  liberal  surface. 

Desiring  to  ascertain  just  how  nearly  a  boiler  could 
be  designed  to  work  upon  the  U-tube  principle  of 
circulation,  after  several  trials  the  model  boiler 
shown  in  Fig.  i  was  produced. 

This  model  was  built  entirely  of  brass.  It  contained 
three  drums  four  inches  in  diameter  and  120  brass 
tubes  one-quarter  of  an  inch  in  diameter.  The  tubes 
were  connected  into  headers  and  into  the  circum- 

1  Contributed  to  Power  by  C.  Hill  Smith. 

I 


BOILERS 


ferences  of  the  drums.  The  heads  of  all  three  drums 
were  made  of  plate  glass,  for  observation  of  the  in- 
terior of  the  boiler  when  making  steam.  It  will  be 
noted  that  the  design  of  the  boiler  closely  resembles 


FIG.  i. 


the  U  shape,  only  that  one  leg  is  considerably  longer 
than  the  other,  and  there  are  two  legs  on  the  side  of 
the  U  where  the  heat  is  applied. 

Each  of  the  three  drums  serves  a  special  function 


WATCHING   A   BOILER   AT  WORK  3 

which  will  be  noted  from  the  description  of  the  experi- 
ments. The  two  legs,  instead  of  being  connected 
together  at  the  top,  as  was  the  case  in  the  U-tube,  are 
connected  by  two  separate  passages,  one  for  the  water 
to  pass  through  and  the  other  for  the  steam. 

In  preparing  for  the  tests  the  boiler  was  mounted 
on  a  stand,  so  that  the  tubes  inclined  from  the  hori- 
zontal 20  degrees,  and  the  whole  was  enclosed  on  all 
sides  by  brass  plates.  Alcohol  lamps  were  placed 
inside  the  casing  at  a  point  to  correspond  with  the 
regular  location  of  grates,  or  at  about  one-fourth  of 
the  distance  between  the  front  headers  and  the  rear 
drum.  The  steam  outlet  was  located  on  the  rear 
drum,  as  was  the  safety  valve,  for  experimental 
reasons,  although  in  actual  practice  the  safety  valve 
would  be  located  on  the  front  drum.  The  feed-pipe 
was  introduced  in  the  rear  drum,  while  the  blow-off 
entered  the  lowest  point  of  the  lower  drum,  which  we 
will  call  the  mud-drum.  The  boiler  was  attached  to 
an  open  condenser. 

The  boiler  being  ready  for  test,  it  was  filled  with 
cold  water  until  the  upper  drums  were  filled  to  one- 
half  their  volume.  Candles  were  placed  behind  one 
head  of  each  of  the  three  drums  for  the  purpose  of 
lighting  the  inside.  The  alcohol  lamps  were  then 
lighted  and  the  boiler  interior  was  ready  to  observe 
through  the  glass  heads  of  the  drums. 

The  first  action  noted  was  in  the  front  drum,  which 
served  as  a  discharge  chamber  for  all  the  steaming 
tubes.  The  tubes  of  the  lower  bank  discharged  into 
it  through  headers,  while  those  of  the  upper  bank  dis- 


4  BOILERS 

charged  into  it  independently.  Many  faint,  oily-white 
streamers  were  seen  to  rise  from  the  nipples  connecting 
the  headers  to  the  front  drum,  passing  upward  to  the 
surface  of  the  drum.  They  resembled  little  streamers 
of  white  smoke.  On  reaching  the  surface  of  the  water 
they  passed  into  the  horizontal  circulating  tubes 
which  connected  the  two  upper  drums.  These  little 
streamers  were  heated  water,  which,  being  lighter  than 
the  water  in  the  drum,  rose  to  the  surface.  This  same 
action  soon  appeared  from  the  ends  of  the  upper  bank 
of  tubes,  the  little  streamers  rising  in  a  similar  manner 
and  passing  into  the  horizontal  tubes. 

By  observing  the  rear  drum,  the  little  streamers 
could  be  seen  coming  into  this  drum  from  the  front 
drum.  Here  they  turned  downward  into  the  vertical 
tubes  which  connected  the  rear  drum  to  the  rear 
headers  and  the  mud-drum.  No  action  could  be 
noted  in  the  mud-drum,  which  fact  seemed  to  indicate 
that  these  currents  of  water  passed  into  the  upper 
tubes  and  thence  into  the  front  drum  again,  as  the 
action  from  these  tubes  appeared  very  much  more 
decided  than  the  action  from  the  nipples,  notwithstand- 
ing the  fact  that  the  lower  tubes  were  nearer  to  the 
flame  than  the  upper  ones.  This  was  undoubtedly 
due  to  the  fact  that  the  heated  currents  of  water 
remained  as  near  the  surface  as  possible,  while  the 
colder  water  passed  to  the  bottom  of  the  boiler,  hav- 
ing greater  specific  gravity. 

Particles  of  sediment  could  be  seen  coming  down 
the  vertical  circulating  tubes  into  the  mud-drum, 
evidently  precipitated  from  the  water  that  was  being 


WATCHING   A   BOILER   AT   WORK  5 

heated.  This  sediment  passed  to  the  bottom  of  the 
drum,  where  it  remained.  A  very  gradual  action  was 
now  noted  in  the  mud-drum  in  the  nature  of  similar 
currents  of  water  coming  down  the  vertical  tubes. 
These  currents  acted  strangely  on  entering  the  drum; 
they  spread  out  on  coming  in  contact  with  the  colder 
and  denser  water  lying  at  the  bottom.  By  placing 
the  finger  on  the  upper  portion  of  the  glass  head  and 
then  on  the  lower,  quite  a  difference  in  temperature 
was  noted.  Little  streamers  of  heated  water  soon 
commenced  to  pass  into  the  lower  bank  of  streaming 
tubes  which  were  connected  into  this  drum.  They 
passed  across  the  drum  with  a  sort  of  shivering  motion. 
A  new  and  very  interesting  phenomenon  was  now 
noticed.  Occasionally  there  would  appear  from  the 
ends  of  the  steaming  tubes  little  rings  of  heated  water, 
which  shot  across  the  drum  with  considerable  velocity. 

The  action  in  the  front  drum  became  very  much 
more  pronounced  and  air  bubbles  appeared  from  the 
nipples  and  tubes.  The  boiler  was  circulating  water 
with  great  rapidity  in  the  same  direction  and  it  was 
noticed,  by  placing  the  hand  on  different  parts  of  the 
boiler,  that  all  parts  were  of  the  same  temperature. 
The  air  bubbles  now  discharged  in  great  quantities 
from  the  tubes  and  nipples  and  rising  to  the  surface 
disturbed  the  water  level  considerably.  It  was  noted 
that  they  floated  along  under  the  surface  of  the  water 
before  they  broke. 

Gradually  these  air  bubbles  ceased  to  appear  and  a 
new  kind  took  their  places.  The  latter  were  steam 
bubbles  and  they  discharged  into  the  drum  with  greater 


6  BOILERS 

velocity  than  the  former.  On  reaching  the  surface 
of  the  water  they  broke  immediately,  but  they  agi- 
tated the  water  level  to  a  much  greater  extent.  Foun- 
tains of  water  would  shoot  up  into  the  drum  for  quite 
a  distance  and  showed  very  vividly  the  conditions 
present  in  the  shell  type  of  boiler,  where  there  are  no 
defined  paths  for  the  water  and  steam  to  travel  and 
nothing  to  prevent  their  conflict  with  each  other. 
This  also  shows  the  cause  for  wet  steam,  and  the  great 
danger  of  entraining  water  with  steam,  as  is  the  case 
where  the  steam  is  removed  from  the  same  place 
where  violent  ebullition  is  present. 

While  the  water  level  in  the  front  drum  was  violently 
agitated,  the  water  level  in  the  rear  drum  remained 
perfectly  calm.  No  steam  was  generated  in  this  drum, 
as  the  horizontal  tubes  connecting  it  to  the  front 
drum  only  circulated  water  that  had  been  freed  of  its 
steam. 

As  the  steam  gage  soon  registered  a  pressure  of  9 
pounds,  the  main  stop-valve  was  opened  to  allow  the 
steam  to  flow  to  the  condenser.  The  abrupt  release 
of  pressure  caused  the  water  to  expand  suddenly  and 
the  water  level  rose  about  one-quarter  of  an  inch.  This 
was  evidently  due  to  the  sudden  generation  of  steam 
caused  by  the  drop  in  the  pressure.  This  increased 
ebullition  caused  a  very  violent  action  in  the  front 
drum  and  the  circulation  of  water  through  the  boiler 
increased  greatly  in  velocity.  The  nipples  and  tubes 
in  the  front  drum  discharged  great  quantities  of 
bubbles.  The  water  level  in  the  rear  drum  during 
this  increase  in  ebullition  showed  but  a  few  ripples, 


WATCHING   A  BOILER   AT   WORK  7 

which  were  evidently  due  to  the  vibration  of  the  steam 
passing  into  the  steam  main,  or  the  discharge  into  the 
water  of  the  open  condenser. 

The  sudden  generation  of  steam  caused  by  the 
opening  of  the  steam  valve  and  subsequent  reduction 
in  pressure,  it  is  believed,  explains  how  the  partial 
rupture  of  the  shell  of  a  return-tubular  boiler  is  ad- 
vanced to  a  disastrous  explosion  by  the  unexpected 
increased  generation  of  steam  due  to  the  lowered 
pressure. 

The  steam  main  was  now  closed  sufficiently  to  allow 
the  boiler  to  operate  on  a  constant  pressure  of  about  6 
pounds.  It  operated  very  smoothly  under  these  con- 
ditions and  made  a  very  interesting  sight  with  the 
steam  generating  in  the  front  drum,  where  the  nipples 
and  tubes  discharged  great  quantities  of  bubbles. 

The  action  in  the  mud-drum  had  in  the  meantime 
become  well  worth  watching.  In  the  other  two  drums 
the  water  showed  clear  in  the  candle  light,  but  the 
color  of  the  water  in  the  mud-drum  was  very  murky. 
Particles  of  sediment  were  noted  settling  to  the  bottom. 
The  withdrawal  of  water  from  this  drum  by  the  steam- 
ing tubes  did  not  appear  to  draw  this  sediment  into 
the  tubes,  as  the  drum  was  of  ample  size  so  that  the 
suction  was  not  felt  at  the  bottom  where  the  sediment 
deposited.  This  emphasized  clearly  the  advantage 
of  a  very  large  mud-drum  to  allow  of  the  thorough 
settling  of  the  sediment. 

The  condition  of  the  front  drum  was  thought  to  be 
too  violent  for  good  practice,  because  the  ebullition 
indicated  restriction  of  circulation.  The  boiler  was 


8  BOILERS 

put  out  of  operation  for  the  purpose  of  making  changes 
in  this  drum  to  prevent  extreme  ebullition.  The  glass 
heads  were  removed  and  other  nipples  inserted  over 
the  nipples  that  connected  the  headers  into  the  drum, 
it  being  here  that  the  most  violent  discharge  of  steam 
was  discernible.  These  new  nipples  were  cut  long 
enough  to  reach  to  the  water  level,  or  just  a  trifle 
below  it. 

The  glass  heads  were  replaced  and  the  boiler  put  in 
operation  again.  The  circulation  was  similar  to  that 
in  the  first  test,  and  no  real  difference  was  noted  until 
the  boiler  commenced  to  make  steam.  Then  it  was 
seen  that  the  ebullition  in  this  drum  was  considerably 
reduced,  the  agitation  that  remained  being  caused 
by  the  discharge  from  the  tubes  of  the  upper  bank. 
This  reduction  was  evidently  due  to  having  provided 
a  channel  through  which  the  water  and  steam  from 
the  nipples  might  flow  to  the  surface  of  the  water  and 
so  prevent  contact  with  the  water  in  the  drum.  As 
the  steam  and  water  no  longer  had  to  force  their  way 
to  the  surface,  the  disturbance  of  the  water  level  was 
naturally  reduced  entirely  in  this  direction.  The  water 
rose  from  the  nipples  in  little  fountains,  the  steam 
disengaging  from  it  in  the  upper  part  of  the  drum. 

The  boiler  was  operated  under  very  severe  condi- 
tions to  try  the  value  of  this  addition  of  nipples.  The 
main  stop-valve  was  suddenly  opened  after  a  consider- 
able steam  pressure  was  obtained.  It  had  very  little 
effect  on  the  water  level  in  this  drum,  only  causing 
the  nipples  to  discharge  fountains  of  water  quite  a 
distance  into  the  drum.  No  water  was  thrown  into 


WATCHING   A  BOILER   AT  WORK  9 

the  superheating  tubes,  as  the  fountains  of  water  dis- 
charged vertically  and  fell  back  immediately  to  the 
water  level. 

The  value  of  this  attachment  being  proved,  the 
boiler  was  blown  down,  and  after  the  water  was  all 
withdrawn  from  the  boiler  considerable  sediment  was 
found  in  the  bottom  of  the  lower  or  mud-drum.  No- 
where else  was  sediment  found,  as  the  drums  offered  no 
opportunities  for  the  sediment  to  settle,  being  pierced 
at  their  lowest  points  by  tubes  and  nipples.  The  tubes 
were  inclined  20  degrees,  which  insured  thorough 
draining  of  the  boiler. 

From  the  foregoing  experiments  many  points  of 
great  value  for  improvement  in  design  of  water-tube 
boilers  can  be  derived.  The  violent  ebullition  in  the 
front  drum  shows  conclusively  that  steam  should  not 
be  withdrawn  from  the  boiler  at  a  point  where  ebulli- 
tion is  present,  on  account  of  the  danger  of  getting 
water  entrained  with  the  steam.  It  also  shows  that 
any  sudden  reduction  of  the  pressure  causes  violent 
ebullition  and  priming.  The  front-drum  conditions 
show  that  this  is  a  good  place  to  locate  the  safety  valve, 
as  the  sudden  opening  of  it  would  cause  no  liability 
of  priming  if  the  steam  is  not  withdrawn  from  this 
drum. 

The  total  lack  of  any  ebullition  in  the  rear  drum 
shows  that  this  is  an  ideal  spot  to  remove  the  steam. 
It  was  noted  that,  owing  to  the  large  amount  of  sepa- 
rating surface  provided,  the  opening  of  the  steam 
valve  caused  no  priming  in  this  drum.  Another  fea- 
ture to  be  noted  is  the  value  of  a  large  mud-drum  to 


I0  BOILERS 

provide  ample  opportunity  for  the  sediment  to  settle, 
and  also  to  provide  a  large  supply  of  water  for  the 
bottom  tubes.  It  would  be  impossible  to  force  the 
boiler  hard  enough  to  drain  this  drum  of  water,  so 
the  danger  of  burning  out  these  tubes  is  eliminated. 

The  provision  of  the  long  nipples  in  the  front  drum 
proved  the  advantage  of  providing  separate  passages 
to  allow  the  steam  and  water  to  reach  the  surface  of 
the  water,  thus  obviating  the  necessity  of  their  forcing 
their  way  to  the  surface  through  the  large  body  of 
water  in  this  drum  and  so  cause  violent  ebullition. 


II 


SIMPLE   TALK   ON    EFFICIENCY    OF 
RIVETED    JOINTS 

MATTER  is  conceived  to  be  composed  of  myriads  of 
tiny  molecules  separated  from  each  other  by  distances 
which  are  very  considerable  as  compared  with  their 
diameters,  and  held  in  fixed  relation  to  each  other  in 
solid  bodies,  by  such  an  attraction  as  holds  the  earth 
to  the  sun  or  the  moon  to  the  earth.  When  we  tear  a 
piece  of  boiler  sheet  apart  it  is  the  attraction  of  these 
molecules  which  we  are  overcoming,  and  if  the  metal  is 
uniform  the  force  required  to  separate  it  will  depend 
upon  the  surface  which  we  expose.  It  will  take  twice 
as  much  force  to  pull  the  larger  of  the  two  bars  in  Fig.  2 
apart  as  it  will  the  smaller,  because  there  is  twice  as 
much  surface  exposed  at  B  as  at  A,  and  the  attrac- 
tion of  twice  as  many  molecules  to  overcome. 

The  force  tending  to  pull  a  body  apart  in  this  way 
is  called  a  "tensile"  force,  and  the  resistance  to  the 
force  necessary  to  pull  a  piece  apart  is  called  its  "ulti- 
mate tensile  strength."  This  is  usually  given  in  pounds 
per  square  inch,  and  is  for  boiler  iron  around  45,000 
and  for  boiler  steel  around  60,000  pounds.  It  should  be 
found  stamped  on  the  sheets  of  which  boilers  are  made. 
Suppose  we  have  a  single  riveted  joint  like  Fig.  3.  We 


12 


BOILERS 


FIG.  2. 


can  divide  it  into  strips  as  by  the  dotted  lines  half- 
way between  the  rivets,  and  consider  one  of  these  strips, 
for  since  they  are  all  alike,  what  is  true  of  one  will  be 
true  of  all.  The  width  of  each  strip  will  be  the  same  as 


FIG.  3. 


EFFICIENCY    OF   RIVETED    JOINTS  13 

the  distance  from  center  to  center  of  the  rivets.  This  is 
called  the  "pitch."  Let  us  suppose  the  pitch  to  be  2\ 
inches,  the  diameter  of  the  rivet  I  inch,  the  thickness  of 
the  plate  i  inch,  the  tensile  strength  of  the  plate  60,000 
and  the  shearing  strength  of  the  rivets  43,000  pounds. 


FIG.  4. 

There  are  two  ways  in  which  this  joint  can  fail:  by 
tearing  the  sheet  apart  where  there  is  the  least  of  it  to 
break,  as  at  a  a  a  a,  Fig.  3,  or  by  shearing  the  rivet  as 
in  Fig.  4. 


If  the  strip  were  whole  as  at  A  in  Fig.  5,  it  would  have 
2j  X  i  =  1.125  square  inches 

of  section,  and  since  it  takes  60,000  pounds  to  pull  one 
square  inch  apart  it  would  take 

1.125  X  60,000  =  67,500  pounds 
to  separate  it. 


I4  BOILERS 

But  i  inch  of  the  sheet  has  been  cut  out  for  the  rivet, 
so  that  there  are  left  only 

2\  -  i  ==  ij  inches 
of  width  to  be  separated,  and 

il  X  i  =  0.625  square  inch 
of  area.    This  would  stand  a  pull  of  only 

0.625  X  60,000  =  37,500  pounds. 

Whether  the  joint  will  part  by  tearing  the  sheet  or 
shearing  the  rivet  depends,  of  course,  on  which  is  the 
stronger.  The  rivet  has 

i  X  i  X  0.7854  =  0.7854  square  inch 

of  area,  and  it  takes  49,000  pounds  to  shear  each  square 
inch,  so  that  it  would  take  a  pull  of 

0.7854  X  49,000  =  38,484.6  pounds. 

to  shear  the  rivet. 

It  is  evident  that  the  rivets  would  go,  then,  long 
before  the  plate,  and  that  the  strength  of.  the  joint 

would  be  o    o    /-       /- 

38,484.6  -f-  67,500  =  0.57 

or  57  per  cent,  of  the  strength  of  the  full  plate. 

But  we  can  add  to  the  rivet  strength  without  reducing 
the  plate  strength  by  putting  in  another  row  of  rivets 
behind  the  first  row.  In  Fig.  6  two  rivets  have  to  be 
sheared,  doubling  the  rivet  strength  without  reducing 
the  plate  strength,  for  the  holes  for  these  extra  rivets 
do  not  reduce  the  plate  section  along  any  one  line  if 
there  is  space  enough  between  the  rows.  In  Fig.  7  the 


EFFICIENCY    OF   RIVETED    JOINTS  15 

sheet  is  no  more  apt  to  part  along  the  line  aaaa  than 
it  would  be  if  the  second  row  of  rivets  were  not  there, 
and  no  more  likely  to  part  on  the  line  bbbb  than  on  the 
other.  Any  strip  of  a  width  equal  to  the  pitch  will 


FIG.  6. 


contain  two  rivets,  whether  we  take  it  through  the 
rivet  centers,  as  at  A,  Fig.  7,  or  at  equal  distance  to 
either  side  of  one  rivet  in  each  row,'as  at  B  in  the  same 
figure.  In  the  first  case  it  includes  one  full  rivet  and 
two  halves,  and  in  the  latter  case  two  full  rivets. 


FIG.  7. 

To  find  the  efficiency  of  this  joint,  then,  we  calculate 

the  efficiencies  of  the  plate  and  use  the  lowest  efficiency. 

To  calculate  the  plate  efficiency,  divide  the  difference 


1 6  BOILERS 

between  the  pitch  and  the  diameter  of  the  rivets  by  the 
pitch. 

This  is  simpler  than  the  operation  which  we  went 
through  above,  which  was 

(pitch-diam.)  X  thickness  X  tensile  strength 
pitch         X  thickness  X  tensile  strength 

the  numerator  being  the  pull  required  to  separate  the 
sheet  with  the  rivet  holes  cut  out,  and  the  denominator 
the  pull  required  to  separate  the  full  sheet.  As  the 
thickness  and  tensile  strength  appear  in  both  numerator 
and  denominator,  they  cancel  out. 

To  find  the  rivet  efficiency,  multiply  the  diameter  of 
the  rivet  by  itself,  by  0.7854,  by  the  shearing  strength  per 
square  inch  and  by  the  number  of  rows,  and  divide  by 
the  product  of  the  pitch,  thickness  and  tensile  strength 
per  square  inch  of  section. 

These  rules  are  applicable  only  to  lap  joints  where 
the  rivets  are  in  single  shear. 


Ill 


SIMPLE  TALKS  ON  THE  BURSTING  STRENGTH 
OF   BOILERS 

THERE  are  two  ways  that  a  shell,  such  as  is  shown 
in  the  sketches  herewith,  might  break  under  internal 
pressure.  The  sheets  might  tear  lengthwise,  letting 
the  shell  separate,  as  in  Fig.  8,  or  they  might  tear 
across,  letting  it  separate  endwise,  as  in  Fig.  9. 


•  8095  i't* 

»80956  1C 

V^ 

FIG.  8. 


FIG.  9. 


Which  is  it  the  more  likely  to  do? 

To  push  it  apart  endwise,  as  in  Fig.  9,  we  have  the 
force  acting  on  the  heads.  This  force  is  the  pressure 
per  square  inch  multiplied  by  the  number  of  square 
inches  in  the  head.  The  area  of  a  circle  is  the  diam- 
eter multiplied  by  itself  and  by  3.1416  and  divided  by 
4;  or  since  3.1416  divided  by  4  is  .7854,  the  area  is  the 
square  of  the  diameter  multiplied  by  .7854. 

17 


l8  BOILERS 

Suppose  the  internal  diameter  of  the  shell  to  be  48 
inches,  and  the  pressure  100  pounds  per  square  inch, 
the  pressure  on  each  head  would  be 

48  X  48  X  .7854  X  100  =  180,956.16  pounds, 

or  over  90  tons.  This  pressure  would  act  on  each  head, 
and  the  effect  would  be  the  same  as  though  two  weights 
of  180,956.16  pounds  each  were  pulling  against  each 
other  through  the  boiler,  as  in  Fig.  10. 


FIG.  10. 

If  the  shell  were  not  heavy  enough  to  stand  the 
strain,  it  would  tear  apart  along  the  line  where  the 
metal  happened  to  be  the  weakest,  as  at  A.  At  first 
sight  it  looks  as  though  the  metal  had  to  sustain  both 
these  forces  or  weights,  and  that  the  stress  upon  the 
shell  would  be  twice  180,956.16  pounds;  but  a  little 
consideration  will  show  that  this  is  not  so.  One  simply 
furnishes  the  equal  and  opposite  action  with  which 
every  force  must  bje  resisted.  A  man  pulling  against 
a  boy  on  a  rope  (Fig.  1 1)  can  pull  no  harder  than  the 
boy  pulls  against  him.  If  he  does  he  will  pull  the  boy 
off  his  feet,  and  the  strain  on  the  rope  will  be  only 
what  one  of  them  pulls,  not  the  sum  of  both  pulls. 
In  order  that  the  man  may  pull  with  a  force  of  50 


BURSTING   STRENGTH   OF   BOILERS  19 

pounds,  the  boy  must  hold  against  him  with  a  force 
of  50  pounds.     Both  are  pulling  with  a  force  of  50 


pounds,  but  the  tension  on  the  rope  is  50  pounds,  not 
100.  The  boy  might  be  replaced  with  a  post  (Fig.  12). 
Now,  when  the  man  pulls  with  a  force  of  50  pounds 


FIG.  12. 


against  the  post,  you  would  not  say  that  there  was 
100  pounds  tension  on  the  rope;  yet  the  post  is  pulling 
or  holding  against  him  with  a  force  of  50  pounds, 


2O 


BOILERS 


just  as  the  boy  did.  In  Fig.  13  it  is  easily  seen  that 
the  tension  on  the  cord  is  50  pounds.  You  would  not 
say  that  it  was  100,  if  the  pull  of  the  weight  were 
resisted  by  another  weight  of  50  pounds,  as  in  Fig.  14, 
instead  of  by  the  floor. 


v 

I  50  Ib3.  I 


FIG.  13. 


FIG.  14. 


The  shell  is  therefore  in  the  case  which  we  have 
imagined  subjected  to  a  force  of  180,956.16  pounds, 
which  tends  to  pull  it  apart  endwise,  as  in  Fig.  10. 

To  resist  this  there  are  as  many  running  inches  of 
shell  as  there  are  inches  in  the  circumference. 

The  circumference  is  3.1416  times  the  diameter,  so 
that  to  pull  the  boiler  in  two 

48  X  3.1416  =  1 50.7968  inches 

of  sheet  would  have  to  be  pulled  apart. 

The  force  exerted  upon  each  running  inch  of  sheet 
would  be  the  pressure  acting  endwise  divided  by  the 
circumference,  or 

180,956.16  4-  150.7968  =  i, 200  pounds. 

The  area  is 

diam.  X  diam.  X  3.1416 

4 


BURSTING   STRENGTH    OF   BOILERS  21 

The  circumference  is 

Diam.  X  3.1416. 
Dividing  the  area  by  the  circumference  we  have 

diam.  X  diam.  X  3.1416  _  diam. 
4  X  diam.  X  3.1416  4 

or  the  strain  on  each  running  inch  of  sheet  per  pound 
of  pressure  is  one-fourth  the  diameter. 


-Diamoter- 


FIG.  15. 

Now  let  us  see  what  it  would  be  in  the  other  direc- 
tion. 

If  we  consider  the  pressure  acting  in  all  directions 
as  in  the  upper  half  of  Fig.  15,  we  should,  to  get  the 
total  pressure  on  the  area,  have  to  multiply  the  pres- 


22  BOILERS 

sure  per  square  inch  by  the  whole  area,  which  would 
be  the  circumference  for  a.  strip  i  inch  wide;  but  if 
we  are  considering  the  effect  of  pressure  in  one  direc- 
tion only,  we  must  consider  only  the  area  in  that 
direction.  If  we  are  studying  the  effect  of  the  pres- 
sure in  forcing  the  shell  in  the  direction  of  the  arrows 
in  the  lower  half  of  Fig.  15,  we  must  consider  only  the 
area  which  comes  crosswise  to  that  direction,  the 
"projected  area,"  as  it  is  called;  the  area  which  the 
piece  would  present  if  we  were  to  hold  it  up  and  look 
at  it  in  the  direction  of  the  arrows  or  of  the  shadow 
which  it  would  cast  in  rays  of  light  running  in  the 
direction  of  the  pressure.  This,  it  will  be  easily  recog- 


FIG.  1 6. 

nized,  is  the  diameter  of  the  boiler  wide  and  i  inch 
high,  as  shown  in  Fig.  15,  so  that  the  number  of  square 
inches  upon  which  the  pressure  is  effective  in  one 
direction  is  equal  to  the  diameter  for  a  strip  i  inch 
wide.  There  is  therefore  a  force  tending  to  pull  each 
i -inch  ring  of  the  shell  apart,  as  in  Fig.  16,  of  48  X  100 
=  4800  pounds,  and  as  this  force  is  resisted  by  two 
running  inches  of  metal, one  at/4  and  one  at  B  (Fig.  i  5), 


BURSTING   STRENGTH   OF   BOILERS  23 

the  stress  per  inch  will  be  4800  ~  2  =  2400  pounds. 
This  is  just  twice  what  we  found  it  to  be  in  the  other 
direction;  and  it  is  plain  that  this  should  be  so,  for 
the  stress  per  pound  of  pressure  tending  to  burst  the 
boiler,  as  in  Fig.  8,  is,  as  we  have  just  seen, 

diam. 


which  is  just  twice  the  -      -  which  we  found  it  to  be 

in  the  other  direction.  It  is  for  this  reason  that  boilers 
are  double  riveted  along  the  side  or  longitudinal 
seams,  while  single  riveting  is  good  enough  for  girth 
seams. 


IV 


SIMPLE   TALKS   ON    THE    BURSTING 
STRENGTH    OF    BOILERS 

IN  the  preceding  chapter  we  found  that  a  cylinder 
equally  strong  all  over,  will  split  lengthwise  with  one- 
half  the  pressure  which  would  be  needed  to  tear  it 
apart  endwise. 


FIG.  17. 

Let  us  see  how  much  pressure  it  would  take  to  burst 
a  shell  of  this  kind.  We  will  consider  a  strip  i  inch  in 
width,  as  in  Fig.  17,  for  the  action  upon  all  the  similar 
strips  into  which  the  boiler  can  be  imagined  to  be 
spaced  off  will  be  the  same.  We  see  that  the  pressure 

24 


BURSTING   STRENGTH   OF   BOILERS  25 

tending  to  pull  the  ring,  i  inch  in  width,  apart  is  equal 
to  the  pressure  per  square  inch  multiplied  by  the 
diameter  of  the  ring.  The  total  pressure  in  all  direc- 
tions, acts  on  the  circumference  as  shown  by  the  radial 
arrows  at  the  upper  portion  of  the  cut,  but  when  we 
come  to  consider  the  force  acting  in  one  direction  we 
must  take  the  projected  area  in  that  direction;  the  area 
of  the  shadow,  as  explained  before,  cast  by  rays  of  light 
flowing  in  that  direction,  and  that  area  would  be  that 
of  the  strip  as  we  see  it  at  the  top  of  Fig.  17,  i  inch 
wide  and  the  diameter  of  the  boiler  long. 

It  is  sometimes  hard  for  one  to  see  why  the  diameter 
is  used  here,  instead  of  the  circumference,  and  a 
further  illustration  is  here  given. 


FIG.  18. 

Suppose  you  had  a  piston  in  an  engine  cylinder 
made  in  steps  like  Fig.  18.  This  would  have  a  good 
deal  more  surface  to  rust  or  to  condense  steam  than 
would  a  flat  piston,  but  it  would  have  no  more  effec- 
tive area  for  the  production  of  power,  would  it?  One 
hundred  pounds  behind  it  in  the  cylinder  would  push 
no  harder  on  the  crosshead  with  this  than  with  a  per- 
fectly flat  piston;  because  the  sidewise  pressure  against 


26 


BOILERS 


the  steps  is  balanced  by  an  equal  pressure  from  the 
opposite  side;  only  the  pressure  on  the  flat  rings  effec- 
tive to  move  the  piston  forward,  and  the  area  of  all 
these  rings  added  together,  is  just  the  same  as  that  of 
a  flat  surface  of  the  same  external  diameter,  as  seen  by 
the  projection  at  the  right. 


FIG.  19. 

This  would  be  just  as  true  if  the  steps  were  a  millionth 
or  a  hundred-millionth  of  an  inch  wide  and  high  instead 
of  an  inch  or  more,  so  that  it  is  just  as  true  of  a  conical 
surface,  like  Fig.  19,  as  of  Fig.  18,  or  of  a  concave 


surface,  like  Fig.  20,  as  of  either;  and  it  is  evident  that 
it  is  the  flattened-out  area  which  one  sees  in  looking 
at  the  object  in  the  line  of  the  force  considered,  the 
projected  area  in  that  direction  as  it  is  called,  and  not 
the  real  superficial  area  which  is  effective. 


BURSTING    STRENGTH   OF   BOILERS  27 

We  have  then  a  force  equal  to  the  pressure  per  square 
inch  multiplied  by  the  internal  diameter  of  the  shell 
tending  to  pull  each  inch  in  length  of  it  apart,  and  we 
have  two  sections,  A  and  B,  Fig.  15,  where  the  sheet 
must  part. 

The  force  tending  to  tear  eacb  of  these  is  the  pressure 
per  square  inch  multiplied  by  the  radius,  or  half  the 
diameter  of  the  shell.  The  resistance  that  the  piece 
of  shell  will  offer  to  being  torn  apart  is  the  tensile 
strength  per  square  inch  multiplied  by  the  number  of 
square  inches  to  be  torn  apart. 


FIG.  21. 

This  area  is  one  inch  long  and  the  thickness  of  the 
sheet  in  width.  The  area  in  square  inches  is  therefore 
the  same  as  the  thickness  in  inches.  If  the  plate  were 
f  of  an  inch  thick,  for  example,  its  section  per  inch  of 
length  would  be  f  of  a  square  inch,  as  shown  in  Fig.  21. 

The  two  opposing  forces,  which  must  be  equal,  not 
only  at  the  point  of  fracture,  but  at  all  times,  are: 

Pressure  per  square  inch  X  radius,  and  pull  per 
square  inch  X  thickness. 

The  pull  on  the  sheet  is  called  the  tensile  force.  If 
we  want  to  find  the  tensile  force  on  the  sheet  for  any 
pressure  per  square  inch,  we  multiply  that  pressure  by 


28  BOILERS 

the  radius  and  divide  by  the  thickness  of  the  sheet  in 
inches. 

If  we  want  to  find  the  pressure  per  square  inch  neces- 
sary to  get  up  a  given  tensile  force  per  square  inch,  we 
multiply  the  given  pull  per  square  inch  by  the  thickness 
of  the  plate  and  divide  by  the  radius  in  inches. 

We  can  find  the  pressure  per  square  inch  necessary 
to  rupture  the  sheet  by  multiplying  the  ultimate  tensile 
strength,  that  is,  the  tensile  force  required  to  pull  a 
square  inch  of  it  apart  by  the  thickness  and  dividing 
by  the  radius. 

Example.  —  What  pressure  would  be  required  to 
burst  a  tank  48  inches  in  diameter,  made  of  steel  \ 
of  an  inch  in  thickness,  having  a  uniform  tensile 
strength  of  60,000  pounds  per  square  inch? 

Tensile  strength  X  thickness 

-^T. — '•  -  =  pressure, 

radius 

60,000  X  .25      ,      ., 

=  625  Ibs.  per  sq.  in. 

But  we  cannot  or  do  not  in  boiler  practice  get  a 
shell  of  uniform  strength.  There  have  to  be  joints  and 
these  joints  are  not  so  strong  as  the  plate  itself.  We 
will  have  a  talk  later  about  how  to  figure  the  strength 
of  a  riveted  joint.  Suppose  the  riveted  joint  was  only 
70  per  cent,  of  the  plate  strength,  then  it  would  take 
only  70  per  cent,  of  the  force  to  pull  it  apart,  and  the 
result  just  found  must  be  multiplied  by  .70  if  the  tank, 
instead  of  having  a  "  uniform  tensile  strength  of  60,000," 
has  a  sheet  strength  of  60,000  and  a  longitudinal  seam 
of  70  per  cent,  efficiency. 


BURSTING   STRENGTH   OF   BOILERS  29 

The  complete  operation  of  finding  the  bursting 
strength  of  a  boiler  shell  is 

Tensile  strength  X  thickness  X  efficiency  of  joint 
radius 

RULE.  —  Multiply  the  tensile  strength  of  the  weakest 
sheet  in  pounds  per  square  inch  by  the  least  thickness  in 
inches  and  by  the  efficiency  of  the  longitudinal  riveted 
joint,  and  divide  by  the  inside  radius  of  the  shell  in 
inches.  The  result  is  the  pressure  per  square  inch  at 
which  the  shell  should  split  longitudinally. 

The  safe  working  pressure  is  found  by  dividing  the 
above  by  the  desired  ''factor  of  safety/'  usually  from 

3-5  to  5. 

This,  it  must  be  noted,  is  the  pressure  at  which  the 
shell  should  fail  in  the  manner  described.  The  boiler 
may  be  weaker  somewhere  else,  as  upon  some  of  the 
stayed  surfaces,  so  that  all  these  points  should  be  con- 
sidered before  the  allowable  pressure  is  fixed  upon. 


SIMPLE  TALKS  ON  THE   BRACING  OF 

HORIZONTAL  RETURN  TUBULAR 

BOILERS 

IN  former  chapters  we  have  discussed  the  strength 
of  a  boiler  so  far  as  the  parting  of  the  shell  is  con- 
cerned, but  even  if  the  shell  is  heavy  enough  and  the 
joint  well  proportioned  the  boiler  may  be  weak  in 
other  respects. 

The  head  of  a  6o-inch  boiler  has  an  area  of 

60  X  60  X  0.7854  =  2827  square  inches. 

At  100  pounds  per  square  inch  there  would  be  a  pres- 
sure against  the  head  of 

2827  X  100  =  282700  pounds.    • 

or  over  140  tons. 

Besides  its  tendency  to  pull  the  shell  apart  endwise, 
this  pressure  tends  to  bulge  the  heads,  as  shown  in 
Fig.  22.  In  the  case  of  a  tank,  or  of  the  drums  of 
water-tube  boilers  where  there  are  no  tubes  in  the 
heads,  they  can  be  made  safe  against  change  of  shape 
under  pressure  by  giving  them  in  the  first  place  the 
shape  that  the  pressure  tends  to  force  them  into;  but 
the  tube  sheet  of  a  horizontal  tubular  boiler,  for  in- 

3° 


HORIZONTAL   RETURN   TUBULAR   BOILERS       31 

stance,  must  be  flat  to  allow  the  tubes  to  enter  square 
with  its  surface.  The  tubes  themselves  act  as  stays 
to  the  lower  part,  but  the  pressure  on  the  part  above 
the  tubes  tends  to  bulge  the  head  and  might  cause 
the  central  tubes  to  pull  out. 


FIG.  22. 

This  is  prevented  by  bracing  the  unsupported  part 
of  the  head  either  by  "through  braces/'  as  in  Fig.  23, 
or  by  "diagonal  braces/'  as  in  Fig.  24. 

In  order  to  find  how  many  braces  are  required,  or  if 
a  given  boiler  is  sufficiently  braced,  the  area  to  be 
braced  must  be  computed.  This  area  may  be  taken 
as  that  included  within  lines  drawn  2  inches  above 
the  top  line  of  tubes  and  2  inches  inside  of  the  shell, 


32 


BOILERS 


HORIZONTAL    RETURN   TUBULAR   BOILERS       33 


34 


BOILERS 


as  in  Fig.  25,  the  area  outside  of  these  lines  being  con- 
sidered to  be  sufficiently  braced  by  the  shell  and  tubes. 
This  figure  is  a  "segment"  of  a  circle  and  its  area  is 
found  by  dividing  its  height  h  by  the  diameter  of  the 
circle,  of  which  it  is  a  part,  finding  the  quotient  in  the 
column  of  " versed  sines"  of  the  accompanying  table, 
and  multiplying  the  segmental  area  as  given  opposite 
that  quotient  in  the  next  column  by  the  square  of  the 
diameter. 


oooooooooo 

!  O  O  O  O  O  O  O  O  O  O  O'; 


FIG.  25. 

For  example,  suppose  the  hight  b  in  Fig.  25  to  be 
1 8  inches  and  the  diameter  of  the  boiler  60  inches. 
The  diameter  of  the  circle  of  which  the  segment  is  a 
part  is  56  inches,  because  we  go  2  inches  inside  the  shell 
on  both  ends  of  the  diameter. 

Following  the   rule  we   divide   the   height   by  the 

diameter 

18  ~  56  =  0.3214. 

The  values  in  the  table  are  given  to  only  three  places 
of  decimals,  but  the  division  should  be  carried  out  to 


HORIZONTAL   RETURN   TUBULAR   BOILP:RS       35 

four  places.  If  the  last  figure  is  less  than  5,  drop  it 
off.  If  it  is  5  and  the  quotient  comes  out  even,  i.e., 
there  is  no  remainder  after  the  5,  drop  it  off,  also.  If 
the  last  figure  is  greater  than  5,  or  in  case  it  is  5,  and 
the  division  did  not  come  out  square,  drop  it  off,  but 
raise  the  third  figure  one. 

In  the  case  in  hand  the  quotient,  0.3214,  conies  be- 
tween the  0.321  and  0.322  of  the  table,  and  is  nearer 
the  0.321,  being  but  0.3214  —  0.321  =  0.0004  °ff» 
while  it  is  0.322  -  0.3214  =  0.0006  off  from  the 
higher  value.  If  it  were  0.3216,  however,  it  would  be 
nearer  0.322  than  0.321. 

The  segmental  area  corresponding  with  0.321  in  the 
table  is  0.2176.  Multiplying  this  by  the  square  of  the 
diameter  gives  56  X  56  X  0.2176  =  682.39  square 
inches  as  the  area  of  the  segment,  and  the  force  to  be 
braced  against  is  this  number  of  square  inches  mul- 
tiplied by  the  pressure  per  square  inch. 

A  through-brace  which  pulls  squarely  on  the  plate 
has  an  effect  in  keeping  it  from  bulging  equal  to  the 
tensile  strain  in  the  brace  itself  —  i.e.,  if  the  brace 
were  under  a  strain  of  6000  pounds,  it  would  tend  to 
pull  the  head  in  and  keep  it  from  bulging  with  an 
equal  force;  but  if  a  diagonal  brace,  as  in  Fig.  26,  were 
under  a  strain  of  6000  pounds,  it  would  tend  to  pull 
the  lug  on  the  head  in  its  own  direction  with  that 
force,  but  would  resist  a  force  in  a  direction  at  right 
angles  with  the  head  of  only  .91  as  much,  or  5,460 
pounds.  This  figure  is  found  by  dividing  the  length 
of  the  line  b  c  by  the  length  of  the  line  a  b. 
.  In  order  to  find  if  a  boiler  is  sufficiently  braced; 


36  BOILERS 

Find  the  smallest  cross-section  of  each  brace  in 
square  inches. 

Multiply  the  cross-section  of  each  diagonal  brace 
by  the  quotient  of  the  distance  of  its  far  end  from  the 
head  in  a  line  perpendicular  to  the  head  (b  c,  Fig.  26), 
divided  by  the  length  of  the  brace. 

Add  all  these  results  together. 


FIG.  26. 

For  such  braces  as  are  all  alike,  as  for  through- 
braces  of  the  same  diameter  of  cross-section,  you  can 
of  course  compute  one  and  multiply  it  by  the  number 
of  similar  ones. 

Divide  the  product  of  the  area  to  be  braced  and  the 
pressure  per  square  inch  by  the  sum  of  all  these  values, 
and  you  will  have  the  strain  on  the  braces  per  square 
inch  of  section. 

The  rules  of  the  United  States  Board  of  Supervising 
Inspectors  allow  a  strain  of  6000  pounds  per  square 
inch  on  the  braces.  If  the  computed  stress  does  not 
exceed  this  amount,  the  boiler  is  sufficiently  braced. 


HORIZONTAL    RETURN   TUBULAR   BOILERS 


To  determine  what  pressure  a  boiler  will  stand,  so 
far  as  its  bracing  is  concerned,  multiply  the  minimum 
cross-section  of  each  brace  by  the  quotient  of  the  dis- 
tance of  its  far  end  from  the  plate  perpendicularly  di- 
vided by  the  length  of  the  brace.  Add  the  results  and 
multiply  by  6000.  Divide  the  produce  by  the  number 
of  square  inches  in  the  segment,  and  the  quotient  will 
be  the  pressure  per  square  inch  that  the  bracing  is  good 
for. 

AREAS  OF  SEGMENTS  OF   CIRCLES 


Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

.1 

.04087 

.121 

.05404 

.142 

.06892 

.163 

.08332 

.101 

.04148 

.122 

.05469 

•143 

.06892 

.164 

.08406 

.102 

.04208 

.123 

•05534 

.144 

.06962 

.165 

.0848 

.103 

.04269 

.124 

.056 

•145 

•07033 

.166 

•08554 

.104 

.0431 

•125 

.05666 

.146 

.07103 

.167 

.08629 

.105 

.04391 

.126 

•05733 

.147 

.07174 

.168 

.08704 

.106 

.04452 

.127 

•°5799 

.148 

•07245 

.169 

.08779 

.107 

.04514 

.128 

.05866 

.149 

.07316 

.17 

.08853 

.108 

•°4575 

.129 

•05933 

•15 

•07387 

.171 

.08929 

.109 

.04638 

•13 

.06 

•J5i 

•07459 

.172 

.09004 

.11 

.047 

•131 

.06067 

.152 

•07531 

•173 

.0908 

.III 

.04763 

.132 

•06135 

•153 

.07603 

.174 

•09155 

.112 

.04826 

•133 

.06203 

•i54 

.07675 

•175 

.09231 

•113 

.04889 

•134 

.06271 

-155 

.07747 

.176 

.09307 

.114 

•°4953 

•J35 

.06339 

•  156 

.0782 

.177 

.09384 

•US 

.05016 

.136 

.06407 

•157 

.07892 

.178 

.0946 

.Il6 

.0508 

•137 

.06476 

•  158 

.07965 

.179 

•09537 

.117 

.05145 

.138 

•06545 

•159 

.08038 

.18 

.09613 

.118 

.05209 

•i39 

.06614 

.16 

.08111 

.181 

.0969 

.119 

.05274 

.14 

.06683 

.161 

.08185 

.182 

.09767 

.12 

.05338 

.141 

-06753 

.162 

.08258 

.183 

.09845 

38  BOTLKRS 

AREAS  OF  SEGMENTS  OF  CIRCLES — Continued 


Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

.184 

.09922 

.216 

.12481 

.248 

.15182 

.28 

.18002 

•185 

.1 

.217 

.12563 

.249 

.15268 

.281 

.18092 

.186 

.10077 

.218 

.12646 

•25 

.15355 

.282 

.18182 

.187 

•IOI55 

.219 

.12728 

.251 

.15441 

.283 

.18272 

.188 

.10233 

.22 

.12811 

•252 

.15528 

.284 

.18361 

.189 

.10312 

.221 

.12894 

•253 

•15615 

.285 

.18452 

.19 

.1039 

.222 

.12977 

•254 

.15702 

.286 

.18542 

.191 

.10468 

.223 

.1306 

•255 

•15789 

.287 

•18633 

.192 

.10547 

.224 

.i3J44 

.256 

.15876 

.288 

.18723 

•193 

.10626 

.225 

.13227 

•257 

.15964 

.289 

.18814 

.194 

.10705 

.226 

•I33n 

•258 

.16051 

.29 

.18905 

•195 

.10784 

.227 

•J3394 

•259 

.16139 

.291 

.18995 

.196 

.10864 

.228 

.13478 

.26 

.16226 

.292 

.19086 

.197 

.10943 

.229 

.13562 

.261 

.16314 

•293 

.19177 

.198 

.11023 

•23 

.13646 

.262 

.16402 

•294 

.19268 

.199 

.IIIO2 

.231 

•I373I 

.263 

.1649 

.295 

.1936 

.2 

.IIl82 

.232 

•13815 

.264 

.16578 

.296 

•I945r 

.201 

.11262 

•233 

.139 

•265 

.16666 

•297 

.19542 

.202 

•II343 

•234 

.13984 

.266 

.16755 

.298 

•19634 

.203 

.11423 

•235 

.14069 

.267 

.16844 

•299 

•19725 

.204 

.H503 

.236 

•I4I54 

.268 

.16931 

•3  ' 

.19817 

.205 

.11584 

.237 

.14239 

.269 

.1702 

.301 

.19908 

.206 

.11665 

.238 

.14324 

•27 

.17109 

.302 

.2 

.207 

.11746 

•239 

.14409 

.271 

.17197 

•303 

.20092 

.208 

.11827 

.24 

.14494 

.272 

.17287 

•304 

.20184 

,2O9 

.11908 

.241 

.1458 

•273 

.17376 

•305 

.20276 

.21 

.1199 

.242 

.14665 

.274 

.17465 

.306 

.20368 

.211 

.12071 

•243 

•i475i 

•275 

•17554 

•307 

.2046 

212 

•I2I53 

•244 

•14837 

.276 

.17643 

•308 

•20553 

2I3 

•12235 

•245 

.14923 

.277 

•17733 

•309 

.20645 

.214 

.12317 

.246 

.  1  5009 

.278 

.17822 

•3i 

.20738 

.215 

.12399 

.247 

.i5095 

•279 

.17912 

•311 

•2083 

HORIZONTAL   RETURN   TUBULAR   BOILERS       39 
AREAS  OF  SEGMENTS  OF  CIRCLES- — Continued 


Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

Versed 
Sine. 

Segmental 
Area. 

.312 

.20923 

•343 

•23832 

•374 

.26804 

•405 

.29827 

.313 

.21015 

•344 

.23927 

•375 

.26901 

.406 

.29925 

.314 

.21108 

•345 

.24022 

•376 

.26998 

.407 

.30024 

•315 

.21201 

•346 

.24117 

•377 

.27095 

.408 

.30122 

.316 

.21294 

•347 

.24212 

•378 

.27192 

.409 

.3022 

•3*7 

.2I387 

•348 

.24307 

•379 

.27289 

.41 

•30319 

.318 

.2148 

•349 

.24403 

•38 

.27386 

.411 

•30417 

•3i9 

•21573 

•35 

.24498 

.381 

•27483 

.412 

•30515 

.32 

.21667 

•351 

•24593 

•382 

.27580 

•413 

.30614 

.321 

.2176 

•352 

.24689 

•383 

.27677 

.414 

.30712 

.322 

•21853 

•353 

.24784 

•384 

•27775 

.415 

.30811 

•323 

.21947 

•354 

.2488 

•385 

.27872 

.416 

•30909 

•324 

.22O4 

•355 

.24976 

•386 

.27969 

.417 

.31008 

•325 

.22134 

•356 

.25071 

•387 

.28067 

.418 

.31107 

.326 

.22228 

•357 

.25167 

•388 

.28164 

.419 

•31205 

•327 

.22321 

•358 

•25263 

•389 

.28262 

.42 

•31304 

.328 

•22415 

•359 

•25359 

•39 

•28359 

.421 

•31403 

•329 

.22509 

•36 

•25455 

•391 

.28457 

.422 

•31502 

•33 

.22603 

•361 

•25551 

•392 

•28554 

•423 

.316 

•331 

.22697 

.362 

.25647 

•393 

.28652 

.424 

.31699 

•332 

.22791 

•363 

•25743 

•394 

.2875 

.425 

•31798 

•333 

.22886 

•364 

•25839 

•395 

.28848 

.426 

-3l897 

•334 

.2298 

•365 

•25936 

.396 

•28945 

.427 

.31996 

•335 

.23074 

.366 

.26032 

•397 

.29043 

.428 

•32095 

•336 

.23169 

•367 

.26128 

.398 

.29141 

.429 

.32194 

•337 

.23263 

.368 

.26225 

•399 

.29239 

•43 

.32293 

•338 

.23358 

•369 

.26321 

•4 

•29337 

•431 

•32391 

•339 

•23453 

•37 

.26418 

.401 

•29435 

•432 

•3249 

•34 

•23547 

•371 

•26514 

.402 

•29533 

•433 

•3259 

•341 

.23642 

•372 

.26611 

.403 

.29631 

•434 

.32689 

•342 

•23737 

•373 

.26708 

.404 

.29729 

•435 

•32788 

VI 


CALCULATING   THE    STRENGTH    OF 
RIVETED   JOINTS1 

IN  calculations  relative  to  the  strength  of  steam 
boilers  and  vessels  of  a  similar  character  for  withstand- 
ing high  pressures,  one  of  the  most  important  points 
to  be  considered  is  the  strength  of  the  seams  where  the 
plates  are  joined.  This  is  not  only  important  to  the 
designer  of  such  vessels,  but  also  to  the  operating 
engineer,  who  is  often  required  to  fix  the  limit  of  pres- 
sure which  should  be  carried  on  the  boilers  under  his 
charge,  and  frequently,  owing  to  increased  output 
without  corresponding  addition  to  the  boiler  capacity, 
it  becomes  necessary  to  carry  the  pressure  as  high  as 
safety  will  permit,  and  in  such  cases  it  is  important  for 
the  engineer  to  be  able  to  fix  this  safe  limit.' 

It  is  the  purpose  in  this  chapter  to  show  how  the 
strength  of  the  various  types  of  joint  generally  used  in 
boiler  construction  may  be  calculated,  and  as  only 
simple  arithmetic  is  required  for  the  calculations,  any 
reader  should  find  no  difficulty  in  understanding  how 
it  is  done,  and  applying  the  principles  to  calculate 
the  strength  of  the  particular  joints  which  may  be  of 
interest  to  them.  To  avoid  the  use  of  formulas,  which 

1  Contributed  to  Power  by  S.  F.  Jeter. 
40 


STRENGTH   OF   RIVETED    JOINTS  41 

are  confusing  to  many,  numerical  examples  will  be 
used  to  illustrate  the  methods  of  making  the  calcula- 
tions, and  for  the  sake  of  uniformity  the  tensile  strength 
of  the  sheets  (which  is  the  strength  to  resist  being 
pulled  apart)  will  be  assumed  as  55,000  pounds  per 
square  inch;  the  shearing  strength  of  the  rivets  (which 
represents  their  resistance  to  being  sheared  through 
by  the  plates  at  right  angles  to  their  length)  will  be 
assumed  as  42,000  pounds  per  square  inch  in  single 
shear,  as  represented  in  Fig.  31,  and  78,000  pounds 
per  square  inch  in  double  shear,  as  represented  in  Fig. 
34.  The  resistance  of  the  rivets  to  crushing  will  be 
assumed  at  95,000  pounds  per  square  inch.  For 
modern  construction  consisting  of  steel  plates  and  steel 
rivets,  the  above  values  are  average  figures. 

It  is  customary  to  express  the  strength  of  a  riveted 
joint  as  a  percentage  of  the  strength  of  the  plates  which 
are  riveted  together.  Thus,  if  the  joint  illustrated  in 
Fig.  35  has  an  efficiency  of  62^  per  cent.,  it  would  mean 
that  any  portion  of  its  length  that  divides  the  rivet 
spaces  symmetrically  would  be  0.625  times  as  strong 
as  a  section  of  the  same  length  through  the  solid  plate. 

POSSIBLE  MODES  OF  FAILURE 

Before  proceeding  to  calculate  a  practical  boiler 
joint,  the  different  ways  in  which  two  pieces  of  plate 
riveted  together  might  fail  should  be  noted.  If  a  piece 
of  boiler  plate,  f  inch  thick  and  2|  inches  wide,  is  placed 
in  the  jaws  of  a  testing  machine,  as  illustrated  in  Fig.  27, 
and  pulled  apart,  it  would  separate  at  some  section  as 
A  A.  If  the  tensile  strength  was  55,000  pounds  per 


42  BOILERS 

square  inch,  the  force  that  would  have  to  be  applied 
to  the  jaws  would  be  55,000  times  the  area  separated 
in  square  inches,  which  in  this  case  is 

2!  X  f  =  H  =  °-9375 
square  inch,  so  that  the  pull  would  be 
pounds.         55-000X0.9375  =  5,  ,562.5 

If  another  piece  of  plate  be  taken,  identical  in  every 


r—f--j          \ 

/                 -    ;      !l 

/ 

SK 

•  V'1  ( 

i  Bfl-B  - 

r   i  S 

\     \     !i       r 

-\                   r 

\ 

hi:    ( 

•j      i~J     L 

J 

~H  u 

P 

FIG.  27. 

•    M 

FIG.  28. 

respect  to  the  first,  except  that  a  hole  i  inch  in  diameter 
is  drilled  through  it  as  illustrated  in  Fig.  28,  and  the 
plate  be  pulled  apart  in  the  testing  machine  as  before, 
it  is  evident  that  it  would  fail  along  the  line  B  B,  as 
the  area  of  the  reduced  section  caused  by  drilling  the 
hole  would  be  only 

(2.5  —  i)  X  0.375  =  0.5625 

square  inch,  and  the  force  necessary  to  pull  it  apart 

would  be 

55,000  X  0.5625  =  30,937.5 


STRENGTH   OF   RIVETED    JOINTS 


43 


pounds,  the  strength  of  the  metal  being  the  same  in 
both  instances.  Now  if  the  relation  between  the 
strength  of  the  solid  plate  and  the  drilled  plate  be 
expressed  by  dividing  the  latter  by  the  former,  the 
result  would  be  ^^  ^ 

51,562.5 

or,  in  other  words,  the  drilled  plate  is  capable  of  sus- 
taining 60  per  cent,  of  the  load  that  could  be  carried 
by  the  solid  plate. 

If,  instead  of  using  a  single  piece  of  plate,  two  plates 
are  drilled  with  i-inch  holes  in  the  ends  and  are  joined 
together  by  a  rivet,  as  shown  in  Fig.  29,  and  an  attempt 


FIG.  30. 


should  be  made  to  pull  them  apart  as  before,  there 
would  be  four  probable  ways  in  which  failure  might 
take  place,  all  of  which  are  considered  in  the  calculation 
and  design  of  riveted  joints.  First,  the  section  of  plate 
each  side  of  the  rivet  hole  might  break,  leaving  the  ends 


44 


BOILERS 


as  shown  in  Fig.  30.  Again,  the  plates  might  shear  the 
rivets  off,  as  illustrated  in  Fig.  31.  Thirdly,  it  has  been 
found  by  practical  tests  of  joints  that  steel  rivets  can- 
not be  subjected  to  a  pressure  much  greater  than 
95,000  pounds  per  square  inch  of  bearing  surface 
without  materially  affecting  their  power  to  resist 
shearing,  and  therefore  the  joint  might  fail,  as  shown 
in  Fig.  31,  due  to  an  excess  crushing  stress  on  the  rivet. 


QD 


oh 


FIG.  31. 


FIG.  32. 


A  fourth  possible  method  of  failure  would  be  for  the 
metal  in  the  sheet  in  front  of  the  rivet  to  split  apart 
or  pull  out,  as  illustrated  in  Fig.  32.  This  latter  mode 
of  failure  is  erratic,  and  cannot  be  calculated,  but  it 
has  been  practically  demonstrated  in  tests  of  joints, 
that  if  the  distance  from  the  edge  of  the  plate  to  the 
center  of  the  rivet  hole  is  i  \  times  the  diameter  of  the 
hole,  this  mode  of  failure  is  improbable,  and  in  the  fol- 
lowing calculations  of  joints  it  will  be  assumed  that 
they  are  properly  designed  to  render  such  failure  im- 
possible. 


STRENGTH   OF   RIVETED    JOINTS  45 

To  determine  the  actual  strength  or  efficiency  of 
such  a  joint  as  is  illustrated  in  Fig.  29,  the  force  re- 
quired to  produce  rupture  must  be  calculated  for  each 
of  the  first  three  ways  mentioned,  and  the  weakest 
mode  of  failure  taken  as  the  maximum  strength  of  the 
joint. 

To  rupture  the  plate  as  illustrated  in  Fig.  30,  the 
pull  required  would  be  the  same  as  to  rupture  the 
drilled  plate  illustrated  in  Fig.  28,  which  was  found 
to  be  30,937.5  pounds.  To  shear  the  rivet  off,  as  in  Fig. 
31,  would  require  a  force  equal  to  the  area  to  be  sheared 
in  square  inches,  times  the  shearing  strength  per  square 
inch;  or  since  the  area  of  a  i-inch  rivet  is  0.7854  square 
inch,  the  force  required  would  be 

0.7854  X  42,000  =  32,987 

pounds.  The  pressure  required  to  cause  failure  by 
crushing  was  stated  to  be  95,000  pounds  per  square 
inch,  and  in  calculating  the  area  exposed  to  pressure 
for  pins  and  rivets,  it  is  figured  as  equal  to  the  diameter 
of  the  pin  or  rivet,  times  the  thickness  of  the  plate; 
therefore,  we  have 

i  X  0.375  =  o-375 

square  inch  of  area  to  withstand  crushing,  or 
0.375  X  95,000  -  35,625 

pounds  would  be  required  to  produce  rupture  of  the 
joint  in  this  manner. 

From  these  figures  it  is  evident  that  the  method 
of  failure  first  considered  is  the  weakest  of  the  three, 


BOILERS 


and,  therefore,  determines  the  efficiency  of  the  joint, 
which  would  be  60  per  cent,  as  found  for  the  drilled 
plate. 

If  one  plate  is  riveted  between  two  other  plates,  as 
illustrated  in  Fig.  33,  the  several  methods  of  failure 
are  calculated  in  the  same  way,  except  for  the  shearing 
of  the  rivet,  which  would  occur  as  shown  in  Fig.  34,  and 


61261  Lbs. 


FIG.  33. 


FIG.  34. 


is  described  as  double  shearing.  While  the  metal 
sheared  in  this  case  would  be  just  twice  as  much  as  in 
single  shear,  it  has  been  found  by  test  that  the  force 
required  is  not  exactly  twice  as  much,  but  1.85  to  1.90 
times  the  amount  in  single  shear;  so  as  stated  at  the 
beginning,  78,000  pounds  per  square  inch  is  .assumed 
for  rivets  in  double  shear  and  42,000  pounds  per  square 
inch  when  in  single  shear. 

Calculating  the  strength  of  a  joint  with  the  dimen- 
sions as  illustrated  in  Fig.  34,  the  strength  of  the  solid 
plate  would  be 

3  X  0.75  X  55,000  =  123,750 
pounds,    The  strength  of  the  center  plate  through  the 


STRENGTH   OF   RIVETED    JOINTS  47 

rivet  hole,  the  failure  being  assumed  similar  to  that 
illustrated  in  Fig.  30,  would  be 

(3  -  i)  X  0.75  X  55,000  =  82,500 
pounds.    The  crushing  strength  of  the  rivet  would  be 
i  X  0.75  X  95,000  -  71,250 

pounds.  The  shearing  strength  of  the  rivet,  or  failure 
assumed  as  in  Fig.  34,  would  be 

0.78154  X  78,000  =  61,261 
pounds. 

From  these  figures  it  is  evident  that  failure  would 
most  likely  occur  as  shown  in  Fig.  34,  and  the  relative 
strength  of  the  joint  as  compared  with  the  solid  plate  is 

61,261 

-  =  0.495, 
123,750 

or  49 J  per  cent.  As  will  be  shown  later,  the  foregoing 
simple  calculations  are  all  that  are  required  to  estimate 
the  strength  of  the  most  complicated  joints. 

THE  UNIT  SECTION 

In  calculating  the  strength  of  a  practical  boiler 
joint,  the  strength  for  the  entire  length  of  a  sheet  could 
be  estimated,  but  this  would  be  laborious  owing  to  the 
number  of  figures  involved  in  the  calculations,  and  the 
same  result  can  be  obtained  by  considering  any  length 
that  divides  the  rivets  symmetrically.  For  convenience, 
the  shortest  length  that  thus  divides  the  rivets  is  the 
one  used  in  such  calculations,  and  this  length  is  called 
a  unit  section  of  the  joint.  When  the  lines  dividing  the 


48  BOILERS 

joint  into  unit  sections  pass  through  a  rivet,  only  one- 
half  of  the  rivet  is  considered  in  the  calculation,  and 
when  rivets  thus  divided  are  lettered  for  reference,  the 
two  halves  on  opposite  sides  will  be  lettered  the  same, 
so  that  referring  to  the  letter  will  indicate  a  whole  rivet. 
Thus,  if  the  rivet  A,  in  Fig.  43,  is  spoken  of,  it  would 
mean  the  combined  halves  of  the  two  rivets  on  the 
outer  row. 

In  measuring  joints  already  constructed  to  obtain 
the  length  of  a  unit  section,  or  the  pitch,  it  should  be 
remembered  that  rivet  heads  do  not  always  drive  fairly 
over  the  center  of  the  rivet  holes,  and  the  rivet  holes 
themselves  are  sometimes  irregular  distances  apart; 
so  it  is  more  accurate  to  measure  a  number  of  pitches 
and  divide  the  distance  by  the  number  measured  to 
obtain  the  average  pitch.  It  will  be  found  most  con- 
venient, where  space  permits,  to  measure  ten  pitches, 
and  then  placing  the  decimal  point  one  figure  to  the  left 
will  give  the  average  unit  length. 

SINGLE-RIVETED  LAP-JOINT 

First  to  be  considered  is  the  single-riveted  lap-joint 
illustrated  in  Fig.  35.  In  a  unit  section  of  2  inches 
one  rivet  is  in  single  shear  and  J  inch  has  been  cut  out 
of  the  plate  by  the  rivet  hole.  The  calculation  for 
strength  is  the  same  as  has  been  made  for  Fig.  38,  and 
the  three  methods  of  failure  to  be  considered  are: 

(1)  Breaking  of  the  section  of  plate  between  the 
rivet  holes,  which  is  called  the  net  section. 

(2)  Shearing  of  a  f-inch  rivet  in  single  shear. 

(3)  Resistance  of  one  rivet  to  crushing. 


STRENGTH   OF   RIVETED    JOINTS 


49 


Using  the   numerical  values  given   in    Fig.   35   the 
following  results  are  obtained: 

(1)  (2  -  0.75)  X  0.25  X  55,000  =  17,187.5  pounds. 

(2)  0.4418  X  42,000  =  18,556  pounds. 

(3)  0.75  X  0.25  X  95,000  -  17,812.5  pounds. 


-  —  — 



rfDU-HoU^    |^l 

6<£ 

^©©©©©CJ)@©(pi 

c 

L 

4x 

FIG.  35. 

Of  the  three  methods  of  failure,  the  first  is  seen  to 
be  the  most  probable,  and  since  a  unit  section  length 
of  the  solid  plate  would  have  a  strength  of 

2  X  0.25  X  55,000  =  27,500 
pounds,  the  efficiency  of  the  joint  would  be 


17,187.5 


=  62.5 


27,500 
per  cent. 

DOUBLE-RIVETED  LAP-JOINT 

Next  in  line  is  the  double-riveted  lap-joint  illustrated 
in  Fig.  36.  There  is  one  feature  connected  with  this 
joint  which  should  be  considered  before  proceeding 
with  the  calculation  of  its  strength.  It  would  evi- 
dently be  possible  to  have  the  two  rows  of  rivets  form- 
ing this  joint  so  close  together  that  the  combined  net 


50  BOILERS 

sections  between  rivets  A  B  and  B  C  would  be  less 
than  between  rivets  AC.  It  has  been  found  in  prac- 
tical tests  of  joints  that  it  is  necessary  to  have  the  com- 
bined area  of  these  two  sections  30  to  35  per  cent,  in 
excess  of  that  between  rivets  A  and  C  in  order  to  be 
sure  that  the  joint  will  fail  along  line  A  C.  This  would 


FIG.  36. 

correspond  to  a  diagonal  pitch  of  two-thirds  of  the 
pitch  from  A  to  C  plus  one-third  of  the  diameter  of 
the  rivet  hole,  or  1.9  inches  in  the  joint  shown  in  Fig. 
36.  Ordinarily,  if  the  rows  are  much  closer  than  this, 
the  joint  has  an  abnormal  appearance  which  would 
be  noted  at  once.  In  further  calculations  it  will  be 
assumed  that  the  joints  are  proportioned  so  that  this 
method  of  failure  will  not  be  possible. 

Proceeding  with  the  calculation  of  the  strength  of 
the  joint  illustrated  in  Fig.  36,  the  methods  of  probable 
failure  to  be  calculated  are  the  same  as  for  the  single- 
riveted  joint: 

(1)  Failure  of  net  section  between  rivet  holes. 

(2)  Shearing  of  two  rivets  in  single  shear. 

(3)  Crushing  strain  on  two  rivets. 


STRENGTH   OF   RIVETED    JOINTS  51 

Using  the  values  given  in  Fig.  36,  we  have  for  the 
above : 

(1)  (2.5      -   0.75)    X   0.3125    X    55,000    =    30,078 
pounds. 

(2)  2  X  0.4418  X  42,000  =  37,112  pounds. 

(3)  2  X  0.75  X  3.5120  X  95,000  =  44>53I  pounds. 

It  is  evident  that  the  first  method  of  failure  is  the 
most  probable,  and  since  the  strength  of  the  solid 

P  at<  2.5  X  0.3125  X  55,000  =  42,969 

pounds,  the  efficiency  of  the  joint  will  be 

30,078 

—7-=  70 
42,969 

per  cent. 

TRIPLE-RIVETED  LAP-JOINT 

In  Fig.  37  is  illustrated  a  triple-riveted  lap-joint. 
Here  the  length  of  unit  section  is  3  inches,  and  the 
different  probable  modes  of  failure  are  identical  with 
those  of  the  single-  and  double-riveted  lap-joints 
except  in  rivet  strength.  It  will  be  noted  that  in  this 
case  there  are  three  rivets  contained  in  each  unit 
section,  which  are  subjected  to  shear  and  crushing. 
The  several  methods  of  probable  failure  to  be  inves- 
tigated are  as  follows: 

(1)  Failure  of  net  section  between  the  rivet  holes 
of  outer  rows. 

(2)  Shearing  of  three  rivets  in  single  shear. 

(3)  Crushing  strain  on  three  rivets. 


52  BOILERS 

Using  the  numerical  values  specified  in  Fig.  37,  we 
Would  have: 

(1)  (3  —  0.75)  X  0.375  X  55,000  =  46,406  pounds. 

(2)  3  X  0.4418  X  42,000  =  55,667  pounds. 

(3)  3  X  0.75  X  0.375  X  95,000  =  80,156  pounds. 


JiDia.  Hole 


FIG.  37. 

The  first  method  of  failure  assumed  is  the  most 
likely,  and  as  the  strength  of  the  solid  plate  for  a  unit 
section  of  length  is 

3  X  0.375  X  55,000  =  61,875 
pounds,  the  efficiency  of  joint  is 

46406  _ 
6i,875~75 

per  cent.  The  triple-riveted  joint  represents  about 
the  maximum  strength  that  can  be  obtained  in  prac- 
tice from  simple  lap-riveted  joints,  as  in  this  form  the 
maximum  pitch  distance  that  permits  proper  calking 
of  the  edge  of  the  plates  is  reached,  and  still  leaving 


STRENGTH   OF   RIVETED    JOINTS 


53 


the  net  section  of  metal  between  the  rivet  holes  the 
weakest  portion  of  the  joint,  so  that  further  addition 
of  rivets  would  not  add  to  its  strength. 

CHAIN  RIVETING 

Joints  illustrated  in  Figs.  36  and  37  have  the  rivets 
arranged  so  that  the  rivets  in  one  row  come  opposite  the 


FTG.  39. 

spaces  in  the  adjacent  rows,  and  this  arrangement  is 
termed  staggered  riveting.  The  same  forms  of  joint  are 
sometimes  made  with  the  rivets  placed  in  straight  rows 
across  the  joint,  is  illustrated  in  Figs.  38  and  39,  which 
is  known  as  chain  riveting.  The  calculations  for  joint 


54 


BOILERS 


efficiency  in  chain-riveted  joints  are  identical  in  every 
respect  to  those  for  staggered  riveting,  and  with  equal 
diameters  and  spacing  of  rivets  and  equal  thicknesses 
of  plate,  the  efficiencies  are  the  same  for  either  type. 

LAP-RIVETED  JOINT  WITH  INSIDE  STRAP 

While  the  lap-riveted  joint  with  inside  strap  is  not 
extensively  used  in  the  manufacture  of  new  boilers,  it 
affords  a  ready  means  of  strengthening  simple  lap 


FIG.  41. 

seams  on  boilers  already  constructed,  and  it  is  quite 
extensively  used  for  this  purpose.  This  joint  is 
illustrated  in  Figs.  40  and  41,  and  it  will  be  seen  that 
it  is  equally  applicable  to  single-  or  double-riveted 


STRENGTH  OF  RIVETED    JOINTS  55 

lap-joints;  it  could  also  be  applied  to  triple-riveted 
joints.  The  joint  illustrated  in  Fig.  40  is  identical  in 
every  respect  with  the  one  shown  in  Fig.  36,  excepting 
the  addition  of  the  fVmch  cover  strip  and  the  outer 
rows  of  rivets,  these  dimensions  being  selected  to  facili- 
tate comparison  between  the  strengths  of  the  two 
joints.  A  unit  section  of  this  joint  is  5  inches  long, 
and  five  methods  of  failure  present  themselves  for 
consideration  in  determining  the  strength  of  the  joint: 

(1)  Breaking  of  the  plate  along  the  section  between 
the  rivet  holes  A  A. 

(2)  The  separation  of  the  plate  along  the  section 
on  line  of  rivets  CD  and  shearing  the  rivet  A. 

(3)  Separation  of  the  plate  along  the  section  on 
line  of  rivets  C  D  and  the  crushing  of  rivet  A. 

(4)  Crushing  of  rivets  A  B  C  D  E  by  the  shell. 

(5)  Shearing  of  rivets  B  CD  E  F  in  single  shear. 
The  pulling  out  of  the  upper  plate,  which  would 

shear  rivet  A  single,  and  E  CD  E  double,  need  not  be 
considered,  since  it  would  evidently  be  stronger  than 
the  first  method  considered  above.  Calculating  the 
value  of  the  possible  methods  of  failure  by  using  the 
dimensions  given  in  Fig.  40,  we  have: 

(1)  (5  -  0.75)  X  0.3125  X  55,000  =  73,040  pounds. 

(2)  [5  -  (2  X  0.75)]  X  0.3125  X  55,000  +  0.4418 
X  42,000  =  78,726  pounds. 

(3)  [5  "  (2  X  0.75)]  X  0.3125  X  55,000  +  0.3125 
X  0.75  X  95,000  =  82,436  pounds. 

(4)  0.3125  X  0.75  X  95,000  X  5  =  ii  1,330  pounds. 

(5)  0.4418  X  42,000  X  5  =  92,780  pounds. 


56  BOILERS 

Evidently  the  next  section  between  the  rivet  holes 
A  A  is  the  weakest  portion  of  the  joint,  and  since  a 
section  of  the  solid  plate  5  inches  long  has  a  strength  of 

5  X  0.3 125  X  55,000  =  85,937 
pounds,  the  efficiency  of  the  joint  is 

S^o  _  8 
percent.  85'937 

Calculation  of  the  joint  illustrated  in  Fig.  41  is  pro- 
ceeded with  in  the  same  manner  as  for  Fig.  40.  It  will  be 
noted  that  to  aid  comparison  the  dimensions  have  been 
assumed  the  same  as  in  Fig.  35  with  the  strap  added. 
The  methods  of  possible  failure  to  be  compared  are: 

(1)  Separation  of  the  plate  along  net  section  G  G. 

(2)  Separation  of  plate  along  section  H  I  and  shear- 
ing of  rivet  G  in  single  shear. 

(3)  Separation  of  plate  along  section  H  I  and  crush- 
ing of  rivet  G. 

(4)  Crushing  of  rivets  G  H  I. 

(5)  Shearing  of  rivets  H  I  J  in  single  shear. 

According  to  the  dimensions  given  in  Fig.  41  the 
numerical  values  would  give  the  following  results. 

(1)  (4  -  0.75)  X  0.25  X  55,000  =  44,687  pounds. 

(2)  [4  -  (2  X  0.75)]  X  0.25  X  55,000  +  0.4418  X 
42,000  =  52,931  pounds. 

(3)  [4  -  (2  X  0.75  )]X  0.25  X  55,000  +  0.75  X 
0.25  X  95,000  =  51,187  pounds. 

(4)  0.75  X  0.25  X  95,000  X  3  ==  53,436  pounds. 

(5)  0.4418  X  42,000  X  3  =  55,668  pounds. 


STRENGTH   OF   RIVETED    JOINTS 

Since  the  strength  of  the  solid  plate  is 
4  X  0.25  X  55,000  =  55,000 
pounds,  the  efficiency  would  be 

£  =  81.25 


57 


5  5  ,OOO 

per  cent. 

It  is  thus  apparent  that  by  adding  a  strap  to  the 
joint  illustrated  in  Fig.  35  and  making  it  like  Fig.  41, 
the  efficiency  has  been  increased  from  62.5  per  cent,  to 
81.25  Per  cent.,  which  would  permit  an  increase  in  steam 
pressure  of  30  per  cent,  on  the  boiler  after  such  change. 

SINGLE-RIVETED  DOUBLE-STRAPPED  BUTT-JOINT 

In  describing  all  forms  of  butt-joints  it  is  customary 
to  refer  to  the  rivets  on  one  side  of  the  butt  only;  thus, 
in  Fig.  42  there  are  actually  two  rows  of  rivets,  but 


FIG.  42. 

•  the  joint  is  only  single-riveted,  for  the  strength  of  the 
joint  along  either  row  is  in  no  wise  dependent  on  the 
other  row.  If  the  two  rows  should  not  be  riveted  alike, 
it  would  be  necessary  to  consider  each  side  as  a  separate 
joint  to  find  which  was  the  weaker,  in  order  to  deter- 


58  BOILERS 

mine  the  strength  of  the  combination.  This,  how- 
ever, is  not  necessary  in  practical  boiler  joints,  since 
they  are  constructed  alike  on  each  side  of  the  butt. 

In  the  joint  illustrated  in  Fig.  42  it  will  be  noted  that 
all  of  the  rivets  are  in  double  shear,  and  only  three 
methods  of  possible  failure  are  presented  for  calcula- 
tion: 

(1)  Breaking  the  net  section. 

(2)  Shearing  of  one  rivet  in  double  shear. 

(3)  Crushing  of  a  rivet  by  the  shell. 

With  the  dimensions  given  in  the  figure  we  have: 

(1)  (2.25    --   0.75)    X   0.3125    X    55,000    ==   25,781 
pounds. 

(2)  0.4418  X  78,000  =  34,460  pounds. 

(3)  0.75  X  0.3125  X  95,000  =  22,230  pounds. 

The  strength  of  the  solid  plate  is 

2.25  X  0.3125  X  55,000  =  38,672 

pounds,  and  since  the  weakest  portion  of  the  joint  is 
the  resistance  to  crushing  of  the  rivets,  the  efficiency  is 

22,230  _ 
38,672  ~  57'5 
per  cent. 

DOUBLE-RIVETED  DOUBLE-STRAPPED  BUTT-JOINT 

Double-riveted  butt-joints  can  be  made  in  two  forms, 
the  one  generally  used  being  illustrated  in  Fig.  43. 
The  calculations  for  the  efficiency  of  this  joint  are  the 
same  as  for  the  single-riveted  joint,  except  that  there 


STRENGTH   OF  RIVETED   JOINTS 


59 


are  two  rivets  to  be  considered  in  each  unit  section 
of  the  joint  instead  of  one.  The  three  methods  of  pos- 
sible failure  are : 

(1)  Pulling  apart  of  the  sheet  along  net  section  A  A. 

(2)  Shearing  of  rivets,  A  B,  in  double  shear. 

(3)  Crushing  of  rivets  A  B. 


r©  ©  ©  ©  © 
©  ©  ©  ©  © 


©.©  ©  ©  © 
i  ©  %$©  ©,B©,  © 

\  w---7s-»r  A         A 


FIG.  43. 

Substituting  the  values  given  in  Fig.  17,  we  have: 

(1)  (2.5    -   0.75)    X   0.3125    X    55,000    =   29,085 
pounds. 

(2)  0.4418  X  78,000  X  2  =  68,920  pounds. 

(3)  0.75  X  0.3125  X  95,000  X  2  =  44,532  pounds. 

The  strength  of  the  solid  plate  is 

2.5  X  0.3125  X  55,000  =  42,969 

pounds,  and  the  weakest  portion  of  the  joint  is  the  net 
section  between  rivets  A  A.     Therefore,  the  efficiency  is 


per  cent. 


42,969 


=  67.6 


6o 


BOILERS 


In  Fig.  44  is  illustrated  the  second  type  of  double- 
riveted  butt-joint.  This  form  of  joint,  if  proportioned 
properly,  can  be  made  considerably  stronger  than  the 
one  illustrated  in  Fig.  43.  There  are  six  methods  of 
possible  failure  to  be  considered: 


FIG.  44. 

(1)  Pulling  apart  of  the  sheet  along  net  section  A  A. 

(2)  Pulling  apart  of  the  sheet  along  section  B  C  and 
shearing  rivet  A. 

(3)  Pulling  apart  of  sheet  along  section-  B  C  and 
crushing  of  rivet  A.     (Note  that  in  calculating  the 
crushing  of  rivet  A  the  thickness  of  the  strap  is  to  be 
used  instead  of  the  plate,  owing  to  the  strap  being 
thinner  than  the  plate.) 

(4)  Shearing  of  rivet  ^single  and  B,  C  double  shear. 

(5)  Crushing  of  rivets  B  C  in  the  plate  and  A  in 
the  strap. 

(6)  Crushing  of  rivets  B  C  in  the  plate  and  shear- 
ing of  rivet  A. 


STRENGTH   OF   RIVETED    JOINTS  61 

Substituting  the  numerical  values  from  Fig.  44,  we 
have: 

(1)  (4  -  0.75)  X  0.3125  X  55,000  =  55,859  pounds. 

(2)  [(4  -•    1.5)   X  0.3125   X   55,000]  +   (42,000  X 
0.4418)   -  61,525  pounds. 

(3)  [(4  -  1.5)  X  0.3125  X  55,000]  +  (0.75  X  0.25 
X  95,000)   ==  60,781  pounds. 

(4)  (42,000  X  0.4418)  -f  (78,000  X  0.4418  X  2)  = 
87,476  pounds. 

(5)  (o./5  X  0.3125  X  95,000  X  2)  +  (0.75  X  0.25 
X   95,000,  =  62,272  pounds. 

(6)  (0.75    X  0.3125    X  95,000   X  2)   +   (42,000   X 
0.4418)   ==  63,087.25  pounds. 

From  these  figures  it  will  be  seen  that  the  net  sec- 
tion between  the  rivet  holes  A  A  is  the  one  most 
likely  to  fail,  and  since  the  strength  of  a  unit  section 
of  the  solid  plate  is 

4  X  0.3125  X  55.000  =  68,750 
ponuds,  the  efficiency  of  the  joint  is 


-  81.25 

per  cent.  68>75O 

TRIPLE-RIVETED  DOUBLE-STRAPPED  BUTT-JOINT 

The  joint  illustrated  in  Fig.  45  is  known  as  the 
triple-riveted  butt-joint.  The  methods  of  failure  to 
be  investigated  are  the  same  as  those  in  Fig.  44,  and 
are  as  follows  : 

(i)    Pulling  apart  of  sheet  at  net  section  A  A. 


62 


BOILERS 


STRENGTH   OF   RIVETED    JOINTS  63 

(2)  Pulling  apart  of  sheet  along  section  C  E  and 
shearing  rivet  A. 

(3)  Pulling  apart  of  sheet  along  section  C  E  and 
crushing  rivet  A. 

(4)  Shearing  rivet  A  single  and  B  C  D  E  double. 

(5)  Crushing  of  rivets  B  C  D  E  in  the  plate  and  A 
in  the  strap. 

(6)  Crushing  of  rivets  B  C  D  E  in  the  plate  and 
shearing  of  rivet  A. 

Substituting  the  values  given  in  Fig.  45 : 

(1)  (7.5  --  i)  X  0.5  X  55,000  ==   178,750  pounds. 

(2)  [(7.5  -  2)  X  0.5  X  55,000]  +  (42,000  X  0.7854) 
=  184,237  pounds. 

(3)  [(7-5    --  2)    X  0.5    X   55>°°o]   +   0    X  0.5    X 
95,000)  =  198,250  pounds. 

(4)  (0.7854  X  42,000)  +  (0.7854  X  78,000  X  4)   = 
278,027  pounds. 

(5)  (i  X  0.5  X  95,000  X  4)  +  0  X  0.375  X  95,000) 
=  225,625  pounds. 

(6)  (i   X  0.5  X  95,000  X  4)  +  (0.7854  X  42,000) 
=  222,987  pounds. 

For  a  unit  length  the  strength  of  the  solid  plate  is 
7.5  X  0.5  X  55,000  =  206,250 

pounds.     The  net  section  between  rivets  A,  A  is  the 
weakest  portion  of  the  joint,  so  that  the  efficiency  is 


per  cent. 


_  86.7 

206,250 


64  BOILERS 

QUADRUPLE-RIVETED  DOUBLE-STRAPPED  BUTT-JOINT 

The  last  type  of  joint  to  be  considered  is  the  quad- 
ruple-riveted butt-joint  illustrated  in  Fig.  46.  This 
joint  is  now  used  on  nearly  all  high-grade  boilers  of 
the  horizontal  return-tubular  type,  and  it  marks 
about  the  practical  limit  of  efficiency  for  riveted  joints 
connecting  plates  of  uniform  thickness  together. 
The  methods  of  failure  to  be  considered  are  practically 
the  same  as  in  the  two  preceding  joints,  except  that 
there  are  more  rivets  concerned  in  the  calculations: 

(1)  Pulling  apart  of  the  sheets  along  net  section 
A  A. 

(2)  Pulling  apart  of  the  sheet  along  section  D  E  F  G 
and  shearing  rivets  ABC. 

(3)  Pulling  apart  of  sheet  along  section  D  E  F  G 
and  crushing  of  rivets  A  B  C  in  the  strap. 

(4)  Shearing  rivets  A  B  C  in  single  shear  and  D 
E  F  G  H  I  J  K  in  double  shear. 

(5)  Crushing  of  rivets  D  E  F  G  H  I  J  K  in  plate  and 
A  B  C  in  the  strap. 

(6)  Crushing  of  rivets  D  E  F  G  H  I  J  K  in  'the  plate 
and  shearing  rivets  ABC. 

Using  the  numerical  values  of  Fig.  46,  we  have: 

(1)  (15.5-  i)  X  0.5625  X  5 5, ooo  =  448, 580  pounds. 

(2)  [(15.5  -  4)  X  0.5625  X  55,000]  +  (3  X  42,000 
X   0.7854)  =  454,739  pounds. 

(3)  [(15.5  -  4)  X  0.5625  X  55>°°°]  +  (3  X  0.4375 
X  i   X  95,000)  =  480,465  pounds. 


FX  RIVETED    JOINTS 

OF  THS 

UNIVERS 


66  BOILERS 

(4)  (3  X  42,000  X  0.7854 )  +  (8  X  78,000  X  0.7854) 
=  589,050  pounds. 

(5)  (8  X  0.5625  X  i   X  95,000)  +  (3  X  0.4375  X 
I   X  95,000)  ==  552,187  pounds. 

(6)  (8  X  0.5625  X   i   X  95,000)  +  (3  X  42,000  X 
0.7854  =  526,461  pounds. 

The  strength  of  the  solid  plate  is 

15.5  X  0.5625  X  55,000  =  479,528 

pounds,  and  the  failure  of  the  sheet  by  pulling  apart 
along  the  net  section  A  A  is  the  one  that  determines 
the  efficiency  of  the  joint,  which  is 

448.580^ 

per  cent.  479.528 

From  the  foregoing  calculations  it  may  be  observed 
that  estimating  the  efficiency  of  riveted  joints,  while 
very  simple,  is  a  rather  tedious  process,  particularly 
if  many  joints  are  to  be  calculated 


VII 


TO  FIND  THE  AREA  TO  BE  BRACED  IN  THE 

HEADS  OF  HORIZONTAL  TUBULAR 

BOILERS 

FOR  the  purpose  of  determining  the  number  of  braces 
to  be  used,  it  is  not  necessary  to  figure  the  area  of  a 
boiler  head  to  a  fraction  of  a  square  inch,  and  a  simple 
rule,  the  reason  for  which  is  so  plain  that  it  can  never 
be  forgotten,  will  be  helpful  to  the  candidate  before 
the  examiner,  or  when  a  table  of  circular  segments  is 
not  to  be  had. 

The  diameter  of  the  boiler  and  the  hight  above  the 
top  row  of  tubes  are  the  only  measurements  which  are 
ordinarily  given.  The  flange  is  considered  good  for 
three  inches  around  the  outside,  and  the  tubes  for  two 
inches  above  their  top  edges,  so  that  the  area  to  be 
braced  is  a  part  of  a  circle  having  a  diameter  six  inches 
less  than  the  given  diameter  of  the  boiler  and  a  hight 
5  inches  less  than  that  of  the  undiminished  segment, 
which  area  is  represented  by  the  shaded  area  in  Fig.  47. 

The  area  of  a  circle  is  the  diameter  multiplied  by 
itself  and  by  0.7854.  It  is  easy,  then,  to  find  the  area 
of  the  circle  of  which  the  shaded  area  is  a  part.  Sup- 
pose We  are  dealing  with  a  72-inch  boiler.  Allowing 
for  3  inches  on  each  end  of  the  diameter,  the  diameter 

67 


68  BOILERS 

of  the  circle  of  which  the  segment  to  be  braced  is  a  part 

would  be  rr  .     , 

72  —  6  =  66  inches, 

and  its  area  would  be 

66  X  66  X  0.7854  =  3421  square  inches; 

and  the  area  of  the  half  circle  abode  would  be  one- 
half  of  this,  or  1710  square  inches. 


FIG.  47. 

Now,  if  from  this  area  the  area  a  b  d  e  is  subtracted, 
the  remainder  will  be  the  required  area  of  the  (shaded) 
portion  to  be  braced.  The  hight  /  g  is  the  radius,  or 
one-half  the  given  diameter  less  the  given  hight  plus  2, 
and  it  will  be  near  enough  if  we  consider  its  length 
equal  to  the  diameter,  as  the  length  of  the  chord  b  d  is 
not  usually  given.  Suppose  the  hight  h  i  to  be  26  inches, 
then  the  hight  /  g  of  the  portion  to  be  subtracted  would 
be 

- 26  +  2  =  inches, 


HORIZONTAL  TUBLAR   BOILERS  69 

and  if  its  length  be  taken  at  66  inches  its  area  will  be 
12  X  66  =  792  square  inches. 

This  is  too  great  by  the  area  of  the  two  little  dotted 
triangles  at  a  b  and  d  e,  but  this  is  so  small  a  proportion 
of  the  total  area  that  it  may  be  neglected,  especially  if 
it  is  borne  in  mind  when  deciding  upon  the  number  of 
braces  that  the  area  as  determined  is  a  little  small. 

Subtracting  this  area  from  that  of  one-half  the  66- 
irich  circle,  as  above  found,  we  have 

1710  —  792  =918  square  inches 

as  the  area  to  be  braced. 

If  the  pressure  is  100  pounds  per  square  inch,  the 
force  to  be  braced  against  is 

918  X  100  =  91,800  pounds, 

and  if  the  braces  used  are  good  for  8000  pounds  apiece, 

it  will  take 

91,800  ~  8000  =11.5  braces. 

We  should  have  to  use  12  braces,  anyway,  and  these 
would  be  good  for 

12  X  8000         ,    .     , 

-  =  960  inches, 
100 

while  the  actual  area  is  936,  instead  of  918,  as  the  above 
approximate  method  made  it.  Unless  the  number  of 
braces  comes  out  very  nearly  square  in  the  calcula- 
tion, there  will  be  enough  leeway  in  using  a  whole 
brace  for  the  fraction  to  make  up  for  the  shortness 
of  the  area.  When  this  fraction  exceeds,  say,  0.9, 
safety  would  be  insured  by  putting  in  an  extra  brace. 


VIII 

GRAPHICAL  DETERMINATION  OF  BOILER 
DIMENSIONS  * 

THE  variables  entering  into  the  design  of  a  steam 
boiler  shell  are  the  working  pressure,  the  diameter 
of  the  shell,  the  thickness  and  tensile  strength  of  the 
plate,  the  diameter,  spacing  and  shearing  value  of  the 
rivets,  the  efficiency  of  the  joints  and  the  factor  of 
safety. 

The  usual  working  pressures  are  80,  100,  125,  and 
150  pounds  per  square  inch. 

The  standard  diameters  of  shell  are  44,  48,  54,  60, 
66,  72,  78,  84,  90  and  96  inches. 

The  tensile  strength  of  the  plate  is  52,000  to  62,000 
pounds  per  square  inch  for  flange  steel  and  55,000  to 
65,000  pounds  per  square  inch  for  fire-box  steel.  The 
average  assumed  for  calculations  is  60,000  pounds  per 
square  inch.  The  shearing  value  of  steel  rivets  is 
38,000  to  42,000  pounds  per  square  inch.  Until 
recently  38,000  pounds  per  square  inch  was  used  for 
all  calculations,  but  this  value  has  been  gradually 
increasing  with  the  improved  quality  of  steel  rivets, 
until  42,000  pounds  per  square  inch  is  now  the  more 
generally  accepted  value. 

1  Contributed  to  Power  by  N.  A.  Carle. 

70 


BOILER   DIMENSIONS  71 

This  has  resulted  in  an  increased  spacing  of  rivets, 
together  with  an  increase  in  the  efficiency  of  the  joints, 
and  a  consequent  reduction  in  the  thickness  of  plate. 

Rivet  holes  are  usually  punched  TV-inch  larger  than 
the  rivets  and  calculated  as  J-inch  larger  than  the 
rivets. 

In  marine  practice,  holes  are  specified  as  drilled  or 
punched  TV~inch  small,  the  shell  assembled  and  the 
holes  then  reamed  to  full  size. 

The  shearing  value  of  the  rivet  is  calculated  for  the 
stock  size  before  driving. 

The  crushing  value  of  steel  rivets  has  been  practi- 
cally eliminated  from  the  problem,  because  in  practice 
the  sizes  selected  give  values  in  excess  of  the  shearing 
value. 

No  consideration  is  given  to  the  friction  of  the  joint, 
it  being  assumed  that  this  is  all  destroyed  before  rup- 
ture, so  that  it  is  not  a  factor  of  the  ultimate  strength. 

The  kind  of  joints  and  size  and  spacing  of  the  rivets 
are  governed  by  accident  insurance  companies'  re- 
quirements and  shop  practice. 

The  size  of  rivets  and  spacing  used  necessary  to 
insure  good  calking  usually  make  the  horizontal  joint 
the  weakest  point  in  the  boiler  and  therefore  the 
governing  factor. 

It  is  desirable  to  get  a  high  efficiency  of  the  joint  for 
high  pressures  and  thick  plates.  Different  types  of 
joints  are  designated  as  single  lap-riveted,  double 
lap-riveted,  triple  lap-riveted,  double  butt-strap- 
riveted,  triple  butt-strap-riveted  and  quadruple  butt- 
strap-riveted. 


72  BOILERS 

The  single  lap-riveted  joint  is  used  on  girth  seams 
generally,  as  the  stress  is  only  one-half  that  on  the 
horizontal  joint,  and  on  the  horizontal  seams  only 
for  very  small  diameters  and  pressures. 

The  quadruple  butt-strap-riveted  joint  is  used  only 
on  very  heavy  plate,  large  diameters  and  high  pres- 
sures. 

The  efficiencies  depend  upon  the  rivet  spacing, 
diameter  of  rivets  and  the  allowances  and  assumptions 
made. 

Design  conditions  reduce  the  problem  to  the  effi- 
ciency of  the  joint  based  on  tearing  between  the  outer 
row  of  rivets. 

The  usual  efficiencies  used  in  calculations  in  the 
shell  formula  are  double  lap,  70  per  cent.;  triple  lap, 
75  per  cent.;  double  butt-strap,  80  per  cent.,  and  triple 
butt-strap,  86  per  cent. 

The  factors  of  safety  ordinarily  used  are  4,  4!  and  5, 
with  6  sometimes  specified  in  marine  practice. 

The  shell  formula  is 

D.  X  W.  P.  X  F.  S.  =  2  X  5.  X  E.  X  *. 

D.  =  Diameter  of  shell  in  inches. 

W .  P.  ==  Working  pressure  in  pounds  per  square  inch. 
F.  S.  =  Factor  of  safety. 

E.  =  Efficiency  of  horizontal  joint. 
/.  =  Thickness  of  plate  in  inches. 

These  are  shown  graphically  in  the  calculating 
diagram  (Fig.  48).  The  use  of  this  diagram  is  probably 
best  illustrated  by  an  example: 

Given.  —  The    boiler    shell    66    inches    in    diameter 


BOILER    DIMENSIONS 


73 


for  a  working  pressure  of  125  pounds  with  a  factor  of 
safety  of  5.  What  thickness  of  plate  is  required  for 
the  shell? 


Assume  that  a  double  butt-strap  joint  will  be  used 
with  an  efficiency  of  80  per  cent.  Starting  with  66 
inches  "diameter  of  shell,"  read  across  to  125  pounds 


74  BOILERS 

"working  pressure/'  then  up  to  a  "factor  of  safety" 
of  5,  and  then  across  to  its  intersection  with  a  vertical 
line  through  80  per  cent,  "efficiency  of  joint."  This 
gives  a  value  slightly  less  than  T7^  inch  for  "thickness 
of  plate." 

Hence  use  T7e  inch  and  by  reading  back  it  will  be 
found  that  this  gives  about  5.1  as  factor  of  safety. 

Usually  the  designer  has  shop  practice  to  follow, 
so  that  instead  of  using  approximate  values  for  the 
efficiency,  the  usual  spacing  and  diameter  of  rivets  can 
be  selected  and  the  actual  efficiency  obtained.  As  an 
example,  assume  that  for  a  double  butt-strap-riveted 
joint  the  shop  spacing  was  4J  inches  and  2\  inches, 
using  ^-inch  rivets.  Read  across  from  4^  inches 
"spacing  of  rivets"  to  ^-inch  rivets  and  then  up  to 
82  per-  cent,  "efficiency  of  horizontal  joint."  The 
boiler  heads  are  made  TV  inch  thicker  than  the  shell, 
as  the  metal  is  decreased  about  this  amount  in  dishing 
and  flanging  the  head.  The  spacing  of  the  girth- 
seam  rivets  is  according  to  shop  practice  and  does  not 
require  a  high  efficiency,  as  the  stress  is  only  one- 
half  that  of  the  shell.  It  is,  therefore,  a  dependent 
factor  in  the  design. 


IX 

THE  SAFETY  VALVE 

THE  study  of  the  safety  valve  has  been  the  first  step 
of  many  a  man  in  scientific  engineering.  Induced  to 
its  study  by  the  necessity  of  solving  its  problems  be- 
fore the  examiner,  his  consideration  of  this  simple 
device  has  led  him  into  the  computation  of  areas,  into 
a  study  of  the  principle  of  the  lever,  of  moments  of 
forces,  of  the  velocity  of  flow  of  steam  and  other 
fundamental  principles  of  mechanics.  This  applies  to 
those  who  have  studied  the  subject  intelligently,  not 
to  those  who  have  attempted  to  get  over  it  by  learning 
a  rule  by  rote,  simply  to  be  confounded  when  con- 
fronted by  another  rule,  or  a  case  to  which  their  rule 
would  not  apply.  The  whole  subject  is  so  simple  that 
an  hour's  study  will  put  a  man  in  possession  of  the 
fundamentals  so  that  he  can  make  his  own  rules  or 
solve  any  problem  without  a  rule,  from  a  sheer  under- 
standing of  the  principles  involved, 

PRESSURE  PER  SQUARE  INCH 

A  cubic  foot  of  water  weighs,  in  round  numbers, 
62  pounds.  If  you  can  imagine  ten  cubic  feet  packed 
one  above  the  other,  as  in  Fig.  49,  they  would  make  a 
column  weighing  some  206  pounds,  supported  on  a 

75 


76 


BOILERS 


\ 


FIG.  40. 


THE  SAFETY   VALVE  77 

base  one  foot  square,  so  that  the  pressure  would  be 
620  pounds  per  square  foot.  The  water  in  a  tank  or 
pond  may  be  conceived  to  be  divided  into  columns  of 
this  kind,  and  it  will  be  seen  that  there  will  be  a  pres- 
sure on  the  bottom  of  62  pounds  per  square  foot  for 
every  foot  of  depth.  But,  in  the  square  foot  support- 
ing this  weight  there  are  144  square  inches;  and  as  the 
pressure  is  evenly  distributed,  each  square  inch 

carries:  , 

62  -T-  144  =  0.43  of  a  pound. 

for  each  foot  in  depth,  and  the  pressure  in  the  case  of 
the  column  10  feet  in  hight  would  be  620  pounds  per 
square  foot,  or  4.3  pounds  per  square  inch. 

Just  as  the  tank  or  pond  could  be  conceived  to  be 
divided  into  columns  of  one  square  foot  section,  each 
square  foot  can  be  conceived  to  be  divided  into  144 
columns  of  one  square  inch  section,  as  shown  in  Fig.  49, 
and  each  foot  in  hight  of  such  column,  like  the  piece 
marked  A,  would  weigh  T|¥  of  the  whole  weight  of  the 
cubic  foot  of  which  it  is  the  T|¥  part,  and  press  upon  its 
square  inch  of  base  with  a  pressure  of: 

62  -f-  144  =  0.43  of  a  pound. 

As  this  pressure  in  a  liquid  or  gas  is  exerted  in  all 
directions,  it  is  evident  that  the  pressure  on  the  hori- 
zontal piston  in  Fig.  50  would  be  4.3  pounds  per  square 
inch,  and  if  it  has  an  area  of  30  square  inches  there 
would  be  a  force  of: 

4.3  X  30  =  129  pounds, 
forcing  the  piston  to  the  right;  and  since  there  is  at  a 


BOILERS 


116.1 

Lbs. 

a  j  b  I 

Depth  in  Pressure  Ibs. 
Feet        persq.in. 
0— r-0 


0.43 


0.86 


1.29 


5  — 


10 


1.72 


—  2.15 


2.58 


3.01 


3.44 


3.87 


4.30 


FIG.  50. 


THE  SAFETY   VALVE 


79 


depth  of  9  feet  a  pressure  of  3.87  pounds  per  square 
inch  the  valve  at  the  left  would  have  3.87  pounds 
pushing  upward  on  each  square  inch  of  its  exposed 
area,  i.e.,  the  area  corresponding  with  the  diameter 
a  b,  and  if  that  area  were  30  square  inches  it  would 

t"i  ICP  * 

30  X  3.87  =  116.1  pounds 

to  hold  the  valve  closed  against  that  pressure. 

The  steam  gage  shows  the  pressure  per  square  inch. 
If  the  gage  points  to  the  100  mark  it  indicates  that  if 
the  pressure  existing  in  the  boiler  Were  exerted  upon 
one  square  inch  of  area,  Fig.  51,  it  would  push  with  a 
force  of  one  hundred  pounds.  If  exerted  upon  an 


l.Inch — 


Unch- 


Unch J 


FIG.  51. 


FIG.  52. 


FIG.  53. 


area  of  one-half  a  square  inch,  Fig.  52,  it  would  push 
with  a  force  of  50  pounds;  upon  an  area  J  inch  square, 
or  1  of  a  square  inch,  Fig.  53,  25  pounds;  upon  an  area 
of  one  square  foot,  or  144  square  inches,  14,400  pounds, 
etc. 

The  force  exerted  by  the  steam  to  lift  a  safety  valve 
depends  then  upon  the  area  of  the  valve  as  well  as 
upon  the  intensity  of  the  pressure. 


8o 


BOILERS 


To  FIND  THE  AREA  OF  A  CIRCLE 

The  area  of  a  i-inch  circle  is  0.7854  of  a  square 
inch,  the  difference,  0.2146,  between  this  and  the  full 
square  of  the  diameter  being  taken  up  by  the  corners, 
Fig.  54.  If  the  side  of  the  square  is  doubled  the  area 


V llnch— - 


-2  Inches- -- 


FIG.  54. 


FIG.  55. 


of  the  square  will  be  multiplied  by  four,  as  is  plainly 
shown  by  Fig.  55,  which  obviously  contains  four 
squares  of  the  area  of  that  shown  in  Fig.  54,  although 
its  side  is  but  twice  as  long;  and  it  is  equally  evident 
that  the  inclosed  circle  bears  the  same  proportion  to 
the  total  area  in  both  cases  and  that  the  shaded  area 
of  the  circle  in  Fig.  55  is  four  times  that  in  Fig.  54, 
although  its  diameter  is  but  twice  that  of  the  smaller 
circle.  If  we  treble  the  length  of  the  sides  the  area  of 
the  square  will  be  multiplied  by  nine,  always  the  square 
of  the  side,  i.e.,  the  side  multiplied  by  itself. 


THE   SAFETY   VALVE 


81 


The  area  of  any  circle  may  be  found  by  multiplying 
the  area  of  a  i-inch  circle  (0.7854)  square  inch  by  the 
square  of  the  given  diameter. 

In  Fig.  55  the  diameter  is  2  inches  and  the  area  is: 

2  X  2  X  0.7854  =  3.1416  square  inches. 
The  area  of  a  4-inch  circle  would  be: 

4  X  4  X  0.7854  =  12.5664  square  inches. 

It  may  aid  in  remembering  the  factor  0.7854  to  know 
that  it  is  one-fourth  of  3.1416,  the  number  by  which 
the  diameter  is  multiplied  to  get  the  circumference. 

The  area  of  a  triangle  is  obviously  one-half  the 
product  of  its  base  and  night.  In  Fig.  530  the  product 


FIG.  530. 


FIG.  536. 


FIG.  53c. 


of  the  base  A  B  and  the  hight  A  C  would  be  the  area 
of  the  rectangle  A  B  C  D  and  the  shaded  area  of  the 
triangle  is  obviously  one-half  of  this,  for  the  two 
unshaded  portions  put  together  would  make  a  similar 
triangle.  This  is  just  as  true  if  the  base  is  an  arc  of  a 
circle  as  in  Fig.  53^,  and  just  as  true  if  the  base  incloses 
the  apex  as  in  Fig.  53^.  The  circle  is  therefore  a 
triangle  with  a  circular  base  3.1416  times  the  diameter 


82  BOILERS 

or  2  X  3.1416  times  the  radius,  and  with  a  hight  equal 
to  the  radius,  and  its  area  (one-half  the  product  of 
hight  and  base)  is: 

A  radius  X  2  X  3.1416  X  radius 

Area  =  -  -|—  =  3.1416  radius2, 

so  that  the  area  equals  3.1416  times  the  square  of  the 
radius,  and  since  the  radius  is  one-half  the  diameter, 
the  square  of  the  radius  is  the  square  of  the  diameter 
divided  by  four: 

Area  =  3.1416  r2  =  3.1416  —  =  D2  X  ^^ 

4  4 

=  0.7854  D2. 

EFFECT  OF  PRESSURE  IN  LIFTING  A  VALVE 

Suppose  the  3-inch  valve  in  Fig.  56  to  be  loaded 
with  six  weights  of  100  pounds  each  and  that  the  valve 
and  steam  weighed  30  pounds,  what  would  the  pressure 
per  square  inch  have  to  be  to  lift  it? 

The  total  weight  to  be  lifted  is  630  pounds.  The 
total  upward  pressure  must  equal  this,  and  if  630 
pounds  is  exerted  on  7.0686  square  inches  (the  area  of 
a  3-inch  valve,  see  table)  the  pressure  on  each  square 

inch  will  be:    ^ 

630  -T-  7.0686  =  89.  i  pounds. 

How  much  load  would  have  to  be  put  upon  the  same 
valve  to  allow  it  to  blow  off  at  75  pounds  per  square 
inch? 

If  the  pressure  exerts  75  pounds  on  one  square  inch, 
it  would  exert  on  the  7.0686  square  inches  of  the  valve 
which  is  exposed  to  it: 


THE   SAFETY   VALVE  83 

75  X  7.0686  =  530  pounds, 

which  must  be  the  combined  weight  of  the  valve  and 
the  weights  with  which  it  is  loaded. 

Fig.  56  does  not  show  a  practicable  valve,  but  is 
sufficient  to  illustrate  the  point  that  the  force  tending 


FIG.  56. 


to  lift  the  valve  must  equal  that  holding  it  to  its  seat 
(in  this  case  the  dead  weight  of  the  valve  itself  and  the 
weights  with  which  it  is  loaded),  and  that  this  upwardly 
acting  force  is  the  area  of  the  valve  in  square  inches, 
multiplied  by  the  pressure  per  square  inch.  Such  a 
dead-weight  valve  is  ponderous  and  impracticable 


84 


BOILERS 


and  the  usual  practice  is  to  use  a  lighter  weight,  increas- 
ing its  effect  by  leverage,  or  to  hold  the  valve  to  its 
seat  with  a  spring. 

THE  PRINCIPLE  OF  THE  LEVER 

Suppose  a  strip  of  board  balanced  over  a  sharp  edge 
as  in  Fig.  57.     If  equal  weights  be  placed  upon  it  at 


h ' 


A 


FIG.  57. 

equal  distances  from  the  center  it  will  still  be  in  bal- 
ance. If  one  of  the  weights  be  moved  in  half  of  the 
distance  to  the  point  at  which  they  are  balanced,  as 
in  Fig.  58,  the  other  weight  will  have  to  be  halved  to 

U 12 >!*- 6 *\ 


FIG.  58. 

preserve  the  equilibrium.  If  one  of  the  weights  be 
moved  to  one-third  of  its  distance  from  the  balancing 
point,  as  in  Fig.  59,  the  other  weight  will  have  to  be 


THE   SAFETY   VALVE  85 

reduced  to  one-third  of  its  original  magnitude  to  pre- 
serve the  balance  at  the  original  distance. 


A 


FIG.  59. 

Notice  that  in  each  case  the  product  of  a  weight  by 
its  distance  from  the  point  over  which  they  balance  is 
the  same  as  the  product  of  the  weight  which  balances 
it  and  its  distance  from  the  same  point.  Suppose  the 
weights  in  Fig.  57  to  be  each  20  pounds,  each  at  12 
inches  from  the  center.  Here  obviously  the  weights 
and  distances  being  the  same  their  products  are  equal: 

20  X  12  =  240      and      20  X  12  =  240. 

When  the  right-hand  weight  is  moved  in  to  6  inches 
from  the  center  the  other  had  to  be   reduced   to    10 

pounds:  , 

10  X  12  =  1 20    and    20  X  6  =  120. 

When  the  left-hand  weight  was  moved  in  to  4  inches 
from  the  center  the  other  had  to  be  reduced  to  6§: 

6§  X  12  =  80    and    20  X  4  =  80. 

The  same  principle  applies  in  Fig.  60,  where  the 
force  exerted  by  the  man,  multiplied  by  the  distance 
A  B,  must,  if  he  lifts  the  machine,  equal  the  pressure 
with  which  the  load  bears  on  the  bar  at  the  point  C, 


86 


BOILERS 


multiplied  by  the  distance  B  C  of  that  point  from  the 
point  B  around  which  the  lever  turns.  In  mechanics, 
this  point,  the  B  of  Fig.  60,  is  called  the  "fulcrum" 
and  the  product  of  the  load,  weight  or  force  by  its 
distance  from  the  fulcrum  is  called  its  "moment." 
In  the  case  described  by  Fig.  57  the  moment  of  each 


FIG.  60. 

weight  is  240;  in  that  of  Fig.  58,  120;  in  that  of  Fig.  59, 
80;  in  that  shown  in  Fig.  60  the  moment  of  the  load  is 
the  weight  or  force  with  which  the  load  bears  on  the 
point  C,  multiplied  by  its  distance  from  the  fulcrum  B, 
and  the  moment  of  the  force  is  the  force  which  the 
man  exerts  upon  the  bar  at  A,  multiplied  by  the  dis- 
tance of  that  point  from  the  fulcrum. 
Notice  that  in  Fig.  61  the  fulcrum  is  at  one  end  of 


THE  SAFETY  VALVE  87 

the  lever  instead  of  between  the  load  and  force  as  in 
the  other  examples.  The  principle  is  the  same.  The 
fulcrum  is  the  stationary  point  about  which  the  load 
and  the  force  move.  In  Figs.  60  and  61  it  is  evident 
that  the  shorter  the  distance  between  the  load  and 
the  fulcrum  the  less  the  man  will  have  to  exert  himself. 


\ 


FIG.  61. 


The  point  to  grasp  and  remember  is  that  the  mo- 
ments must  be  equal  in  order  for  the  force  to  balance 
or  lift  the  load. 

Equal  Moments  Produce  Equilibrium 
There  are  four  important  things  about  a  lever: 


88  BOILERS 

L    -the  load. 

F   =  the  force  applied  to  balance  or  overcome  the 

load. 

Dt  =  distance  of  the  load  from  the  fulcrum. 
Df  =  distance  of  the  force  from  the  fulcrum. 

If  any  three  of  these  are  known  the  third  can  be 
easily  determined,  for,  as  has  been  just  explained, 

Force  X  distance  of  force  =  load  X  distance  of  load. 

P  X  D  =  L  X  DI 
Moment  of  force  =  moment  of  load. 

To  find  the  force  required  to  lift  a  given  load: 
FORMULA:  T  vx  ^ 


RULE.  —  Multiply  tie  load  by  its  distance  from  tie 
fulcrum,  and  divide  by  tie  distance  at  which  tie  force  is 
applied  from  tie  fulcrum. 

To  find  the  distance  at  which  a  given  force  must 
be  applied  from  the  fulcrum  to  balance  a  given  load: 

FORMULA:  T       n 

Df=    ^- 


RULE.  —  Multiply  tie  load  by  its  distance  from  the 
fulcrum  and  divide  by  tie  given  force. 

To  find  the  load  which  may  be  lifted  with  a  given 
force  : 

FORMULA:  r      n 

T       r  \  Uf 


THE  SAFETY  VALVE  89 

RULE.  —  Multiply  the  given  force  by  the  distance  of 
its  point  of  application  from  the  fulcrum  and  divide  by 
the  distance  of  the  load  from  the  fulcrum. 

To  find  the  distance  at  which  a  given  weight  or  load 
must  be  placed  from  the  fulcrum  to  balance  a  given 
force : 

FORMULA:  D  =  F  X  D/ 

Li 

RULE.  —  Multiply  the  given  force  by  the  distance  of 
its  point  of  application  from  the  fulcrum  and  divide  by 
the  load. 

THE  LEVER  SAFETY  VALVE 

Effect  of  the  Leverage  of  the  Ball 
Suppose  the  weight  instead  of  setting  directly  upon 


1    i 


FIG.  62. 


the  valve,  as  in  Fig.  56,  is  applied  through  a  lever,  as 
in   Fig.  62.     From  what  has  preceded  it  will  easily 


go  BOILERS 

be  seen  that  the  weight  multiplied  by  its  distance 
from  the  fulcrum  will  equal  the  force  which  it  will 
exert  upon  the  valve  stem  multiplied  by  the  distance 
of  its  point  of  application  from  the  fulcrum. 


Weight 

f 

Distance 
of  ball 

Pressure 
of  ball 

i 

1 

Distance 
of  stem 

of 
ball 

X 

from 

= 

on 

from 

L/dll 

fulcrum  . 

stem 

I  fulcrum  . 

Let  the  weight  equal  75  pounds, 

distance  of  weight  from  fulcrum  32  inches, 
distance  of  stem  from  fulcrum  2f  inches, 

what  will  be  the  force  exerted  by  the  ball  to  hold  the 

valve  to  its  seat? 

Weight  of  ball  X  Distance  of  ball  from  fulcrum  _ 

Distance  of  stem  from  fulcrum 
Pressure  of  ball  on  stem. 

Then  the  moment  of  the  ball  is: 

75  X  32  =  2400  inch-pounds, 

and: 

2400  -f-  2.75  =  872.727  pounds 

will  be  the  pressure  on  the  valve  stem  due  to  the  ball 
and  the  moments  will  be  equal: 

75  X  32  =  2400    and     872.727  X  2.75  =  2400. 

Suppose  this  to  be  a  4-inch  valve,  the  area  of  which 
is  12.5666  square  inches.  The  pressure  per  square 
inch  upon  the  under  side  of  the  valve  necessary  to 
balance  the  effect  of  the  ball  would  be: 


THE  SAFETY   VALVE  91 

872.727  ~  12.5666  =  69.4  pounds. 

This  is  the  pressure  at  which  the  valve  would  blow 
off  if  nothing  but  the  ball  were  holding  it  to  its  seat. 
It  takes  a  little  additional  pressure  to  lift  the  valve  and 
to  overcome  the  weight  of  the  lever,  as  will  be  explained 
later,  but  this  is  a  comparatively  small  affair  and 
in  usual  approximate  calculations  is  not  taken  into 
account.  Neglecting  these  we  can  make  the  follow- 
ing simple 

Rules  for  lever  safety  valve,  neglecting  weight  of 
valve,  stem  and  lever: 

Let  W  =  weight  of  the  ball, 

D  =  distance  of  ball  from  fulcrum, 
A  =  area  of  valve  in  square  inches, 
d  =  distance  of  stem  from  fulcrum, 
P  =  pressure  per  square  inch  on  valve  which 
will  balance  ball. 

To  determine  the  pressure  on  a  valve  of  given 
diameter  required  to  balance  a  ball  of  given  weight  at  a 
given  distance  from  the  fulcrum. 

F°RMULA:  W  XD 


P  = 


Axd 


RULE.  —  Multiply  the  weight  of  the  ball  by  its  dis- 
tance from  the  fulcrum.  Multiply  the  area  of  the  valve 
in  square  inches  by  the  distance  of  its  stem  from  the 
fulcrum.  Divide  the  first  product  by  the  second  and  the 
quotient  will  be  the  pressure  per  square  inch  required  to 
overcome  the  weight  of  the  ball. 


92  BOILERS 

EXAMPLE.  —  The  stem  of  a  4-inch  safety  valve  is  2 J 
inches  from  the  fulcrum.  Supposing  the  valve  will  blow 
when  the  gage  shows  7  pounds  without  any  weight  upon 
the  lever  (i.e.,  that  it  takes  7  pounds  per  square  inch  on 
the  area  of  the  valve  to  overcome  its  own  weight,  that 
of  the  stem  and  the  bearing  effect  of  the  empty  lever), 
at  what  pressure  would  it  blow  with  a  weight  of  75 
pounds  (Fig.  62)  32  inches  from  the  fulcrum? 

BY  THE  FORMULA: 

P  WA^Di  = 777^ =  69-4  +  7  =  76.4  pounds. 

A  X  d       12.5666  X  2.75 

BY  THE  RULE: 

Area  of  valve  12.5666      75   Weight  of  ball 

Distance  of  stem  2.75      32   Distance  of  ball 

628330     1 50 
879662    225 
251332 


34.558^)2400.00)69.4  pounds. 

This  is  the  pressure  required  to  lift  the  ball.'  Adding 
the  7  pounds  required  to  blow  the  valve  without  the 
ball,  the' answer  would  be  76.4  pounds.  Scratching  out 
the  last  three  figures  of  the  first  product  saves  hand- 
ling large  numbers  and  does  not  materially  affect  the 
result.  If  we  called  this  34.6  (nearer  right  than  34.5 
because  the  58  rejected  is  over  one-half)  the  quotient 
would  still  be  69.36. 

To  find  the  weight  required  to  hold  a  given  pressure 
on  a  given  valve: 


THE  SAFETY  VALVE 


93 


FORMULA: 


D 


RULE.  —  Multiply  the  area  by  the  pressure  and  by  the 
distance  of  the  stem  from  the  fulcrum  and  divide  by  the 
distance  of  the  ball  from  the  fulcrum.  The  quotient  will 
be  the  weight  of  ball  required  to  balance  the  steam  pressure 
on  the  valve. 

EXAMPLE.  —  What  weight  of  ball  would  be  required 
to  allow  the  valve  in  the  above  example  to  blow  off 
at  80  pounds? 

The  ball  must  provide  for  73  pounds  per  square  inch, 
the  lever  valve  and  stem  taking  care  of  the  other 
seven,  so  that  P  =  73  pounds. 

BY  THE  FORMULA: 


.  y8.8  pounds. 


BY  THE.  RULE: 


73 


Pressure 


Distance  of  stem 


376998 
879662 

917-3618 

?75 

45868090 
64215326 
18347236 
Distance  of  ball,     32)2522.744950(78.8  pounds. 

To  find  the  position  of  the  weight  in  order  that  it 
may  exert  a  given  pressure  on  the  stem : 


94  BOILERS 

FORMULA:  _  AxPxd 

W 

RULE.  —  Multiply  the  area  by  ihe  pressure  and  by  the 
distance  of  the  stem  from  the  fulcrum  and  divide  by  the 
weight  of  the  ball.  The  quotient  will  be  the  distance  at 
which  the  ball  must  be  from  the  fulcrum  in  order  to  produce 
a  given  pressure  on  the  stem. 

EXAMPLE.  —  If  the  original  75-pound  weight  had 
been  used,  at  what  distance  from  the  fulcrum  would  it 
have  had  to  have  been  placed  to  have  allowed  the  valve 
to  blow  off  at  80  pounds? 

BY  THE  FORMULA: 

D  .  ^y  =  ".566x^73x3.75  =  3?  6  jnches. 

BY  THE  RULE. — The  product  of  the  factor  in  the 
numerator  is  2522.74495  as  before,  and  dividing  this 
by  75,  the  weight  of  the  ball: 

75)2522.74495  (33.6  inches. 

These  simple  rules  will  serve  all  practical  purposes, 
especially  if  it  is  borne  in  mind  that  P  represents  the 
pressure  with  which  the  ball  only  bears  upon  the  stem, 
not  including  the  weight  of  the  valve,  lever,  etc.,  and  an 
allowance  be  made  for  these  other  effects  as  has  been 
done  in  the  examples.  A  general  idea  of  what  the  pres- 
sure per  square  inch  required  to  lift  the  valve,  stem  and 
lever  may  be  is  given  in  column  8  of  the  table  on  page 
119.  It  is  well,  however,  to  know  how  to  make  these 
allowances  accurately,  and  they  will  now  be  considered. 


THE  SAFETY  VALVE  95 

EFFECT  OF  THE  WEIGHT  OF  THE  VALVE 
AND  STEM 

The  pressure  acts  directly  upon  the  valve  and  stem 
without  leverage,  and  must  exert  a  force  to  balance 
their  weight  equal  simply  to  that  weight,  just  as  was 
the  case  in  Fig.  56. 

Suppose  the  valve  and  stem  of  a  3-inch  valve  to 
weigh  1.5  pounds,  how  much  pressure  per  square  inch 
would  be  required  to  lift  the  valve  from  its  seat? 

Comparing  Figs.  56  and  63,  it  will  be  seen  that  this 
case  is  the  same  as  the  first  example  given  in  describing 
the  earlier  cut.  The  total  pressure  on  the  valve  must  be 
1.5  pounds,  and  if  1.5  pounds  is  to  be  exerted  on  7.0686 
square  inches,  the  pressure  per  square  inch  will  be: 

1.5  -f-  7.0686  =  0.212  pound. 

Column  3  of  the  table  on  page  119  gives  roughly 
the  weights  of  valve  and  stem  used  on  valves  of  the 
standard  diameters  of  three  makers,  and  in  connection 
with  column  4,  which  gives  the  pressure  per  square 
inch  required  to  lift  the  valves  of  the  given  weights, 
serves  to  indicate  the  relative  importance  of  this  factor 
of  the  problem. 

THE  EFFECT  OF  THE  LEVER 

The  weight  of  the  lever  tends  to  hold  the  valve  upon 
its  seat.  It  is  evident  that  it  would  take  a  considerable 
pull  to  lift  the  lever  of  a  large  safety  valve  with  a  cord 
attached  at  the  point  at  which  the  pin  bears,  as  in  Fig. 
64,  and  this  pull  as  measured  upon  a  scale  would  be 


96 


BOILERS 


the  force  which  the  valve  would  have  to  exert  to  push 
the  lever  up.  Every  successive  particle  in  the  length 
of  the  lever  is  acting  with  a  different  leverage,  so  that  it 


FIG.  63. 

would  at  first  appear  a  complicated  process  to  calculate 
this  force;  but  a  body  acts  in  this  respect  just  as  though 
its  whole  mass  were  concentrated  at  its  center  of  gravity 
and  this  makes  the  problem  very  simple. 


THE  SAFETY  VALVE 


97 


If  the  lever  be  taken  off  and  balanced  over  an  edge, 
as  in  Fig.  65,  the  center  of  gravity  will  be  at  the  point 


FIG.  64. 

above  the  knife  edge  when  the  lever  is  balanced,  and  the 
effect  of  the  lever  would  be  the  same  as  if  all  the  mass 
were  concentrated  at  that  point. 


FIG.  65. 

Now  find  the  distance  of  the  center  of  gravity  from 
the  fulcrum,  from  the  point  around  which  the  lever 
turns.  This  will  be  from  the  center  of  the  hole  when  it 
turns  upon  a  pin,  as  in  Fig.  66,  or  from  the  point  where 
it  bears  if  a  knife  edge  is  used,  as  in  Fig.  67;  the  dis- 
tance a  c  in  each  case. 


98 


BOILERS 


In  measuring  for  moments  the  distances  must  be 
taken  on  a  line  passing  through  the  fulcrum  and  at 


o- 


FIG.  66. 


right  angles  to  the  direction  of  the  force.     In  the  case 
of  the  lever  safety  valve  the  holding-down  force  is 


FIG.  67. 

gravity,  which  acts  vertically.    A  line  at  right  angles 
to  the  vertical  is  horizontal,  so  that  distances  should 


A      B 


FIG.  68. 


be  measured  in  a  horizontal  direction  as  through  ABC, 
Fig.  68,  and  not  on  the  lines  x  x  or  y  y. 


THE  SAFETY  VALVE  99 

In  determining  the  distance  a  c,  Figs.  66  and  67,  do 
not  get  bothered  about  the  piece  of  lever  which  extends 
back  of  the  fulcrum.  The  more  metal  there  is  back  of 
this  point  the  nearer  the  center  of  gravity  is  to  the 
fulcrum.  If  there  were  as  much  weight  to  the  left  of  the 
pin  in  Fig.  65  as  to  the  right,  the  center  of  gravity 
would  be  at  the  pin;  the  lever  would  balance  over  the 
pin  as  it  did  over  the  knife  edge  and  not  bear  on  the 
stem  at  all. 

To  apply  this,  suppose  that  the  lever  of  a  3-inch  valve 
v/eighed  six  pounds,  that  the  distance  a  c,  Fig.  66,  be- 
tween the  fulcrum  and  the  center  of  gravity  was  found 
to  be  15  inches,  and  the  distance  a  b  from  the  fulcrum 
to  the  point  at  which  the  pin  bears  2\  inches.  The 
moment  of  the  lever  must  be : 

6  X  1 5  =  90  inch-pounds. 

The  moment  of  the  lifting  force  must  equal  this,  and 
that  moment  is  i\  times  the  force.     Then  the  force 

must  be: 

90  -f-  2\  =  40  pounds, 

2-J-  X  40  =  90      and       15X6  =  90. 

Since  a  force  of  40  pounds  is  to  be  exerted  upon 
7.0686  square  inches,  the  force  per  square  inch  would 

40  -v-  7.068  =  5.66  pounds. 

The  combined  effect  of  the  valve  and  stem  and  of 
the  lever  of  the  3-inch  valve  in  question  would  be: 

0.212  +  5.66  =  5.87  pounds. 
Columns  5  and  6  of  the  table  already  referred  to  give 


zoo  BOILERS 

the  weights  of  levers  and  the  distances  of  their  centers 
of  gravity  from  the  fulcrum  as  ordinarily  found,  and 
column  7  gives  the  pressure  per  square  inch  on  the  valve 
necessary  to  lift  such  levers.  Column  8  gives  the  sum 
of  the  respective  values  in  columns  4  and  7,  i.e.,  the 
pressure  per  square  inch  required  to  lift  the  valve  and 
stem  and  the  lever.  It  will  be  seen  that  the  values  run 
fairly  even  for  all  sizes  of  valves,  and  that  by  using 
seven  or  eight  pounds  as  an  allowance  as  in  the  above 
examples,  results  can  be  attained  with  the  simple  rules 
which  will  be  within  a  pound  or  two  of  right. 

SPRING-LOADED  OR  POP  SAFETY  VALVES 

A  rule  for  calculating  the  pressure  at  which  a  spring- 
loaded  valve  will  blow  off  is  sometimes  asked  for. 
There  are  none  reliable  that  do  not  involve  the  deter- 
mining by  experiment  of  the  force  required  to  com- 
press the  spring,  and  if  you  are  going  to  do  this  you  may 
as  well  determine  by  experiment  at  what  pressure  the 
valve  will,  blow  off.  In  practice  nobody  thinks  of  com- 
puting the  spring-loaded  valve.  If  they  want  it  to  blow 
off  at  1 20  pounds  they  procure  a  suitable  spring  from 
the  makers  and  turn  down  upon  the  binding  nut  until 
the  valve  will  blow  experimentally  at  the  desired  pres- 
sure. The  pressure  at  which  a  spring  will  yield  depends 
not  only  upon  the  shape  and  size  of  the  material  of 
which  it  is  made,  the  diameter,  number,  and  pitch  of 
the  coils,  all  of  which  are  measurable  and  determinable, 
but  upon  the  nature  and  condition  of  the  material  itself. 
You  can  readily  appreciate  that  a  spring  of  brass  would 
compress  with  less  pressure  than  one  of  steel,  similar  in 


THE  SAFETY  VALVE 


101 


every  other  respect,  and  that  there  is  such  a  wide  differ- 
ence in  steels  that  there  will  be  a  great  deal  of  difference 
in  the  action  of  steel  springs  according  to  the  kind  of 
metal,  degree  of  temper,  etc.  The  best  rule  known  is 
the  following: 

To  find  at  what  pressure  a  valve  will  lift  with  a 
spring  of  given  dimensions  and  compression: 

Multiply  the  compression  in  inches  by  the  fourth  power 
of  the  thickness  of  the  steel  in  sixteenths  of  an  inch,  and 
by  22  for  round  or  30  for  square  steel.  Product  I. 


FIG.  69. 

Multiply  the  cube  of  the  diameter  of  the  spring, 
measured  from  center  to  center  of  the  coil  (as  on  the  line 
d,  in  Fig.  69)  in  inches,  by  the  number  of  free  coils  in 
the  spring,  and  by  the  area  of  the  valve  in  square  inches. 
Product  II. 

Divide  Product  I  by  Product  II  and  the  quotient  will 


102  BOILERS 

be  the  pressure  per  square  inch  at  which  the  valve  will 
blow  off. 

The  weight  of  the  valve  and  of  the  spring  should  in 
strictness  be  added  to  Product  I,  when  the  construction 
is  such  that  the  valve  supports  the  spring;  but  inasmuch 
as  the  values  22  and  30  are  guessed  at  it  will  not  pay 
to  go  into  refinements  in  other  directions.  The  result 
of  this  rule  has  never  been  compared  with  an  actual 
valve.  It  is  based  on  a  formula  adopted  by  a  com- 
mittee of  Scotch  engineers  and  shipbuilders.  Corre- 
spondence with  the  manufacturers  of  pop  safety  valves 
as  to  the  accuracy  of  the  formula  brings  out  the  fact 
that  they  proportion  and  calibrate  their  springs  only 
by  experience  and  experiment.  However,  this  rule 
is  given  for  what  it  is  worth.  If  you  have  a  spring- 
loaded  valve  calculate  it  by  this  rule  and  see  how  nearly 
it  comes  to  the  point  at  which  the  valve  will  blow  off. 

With  a  dead  weight  or  a  lever-loaded  valve  the  force 
required  to  lift  it  remains  the  same,  no  matter  how  high 
the  valve  lifts.  The  weights  weigh  no  more  if  they  are 
raised  an  inch  or  two,  and  the  leverage  does  not  change, 
but  with  the  spring-loaded  valve  the  more  the  valve 
lifts,  the  more  the  spring  is  compressed,  and  the  more 
force  is  required  to  compress  or  hold  it.  It  follows  then 
that  if  an  ordinary  valve  were  loaded  with  a  spring  it 
would  simply  crack  open  and  commence  to  sizzle  when 
the  pressure  equaled  the  force  at  which  the  spring  was 
set,  and  that  if  this  were  not  enough  to  relieve  the  boiler 
the  pressure  would  have  to  increase,  opening  the  valve 
more  and  more  until  the  steam  blew  of?  as  fast  as  it  was 
made. 


THE  SAFETY  VALVE 


103 


COMPLETE  SAFTEY-VALVE  RULES 

It  is  evident  that  any  complete  rule  for  the  safety 
valve  must  include  the  separate  treatment  of  the  valve 
and  stem,  the  lever  and  the  ball  as  factors  in  holding 
the  valve  to  its  seat. 

moment  of  ball 


Moment  of  the 
lifting  force 


moment  of  lever 


moment  of  valve  and  stem. 


The  lifting  force  consists  of  the  pressure  per  square 
inch  into  the  area  of  the  valve,  and  its  moment  is  the 
product  of  the  force  by  its  distance  from  the  fulcrum. 
Expanded,  then,  the  above  becomes: 

Weight  of  ball  X  distance  of 
its  center  of  gravity  from  the 
fulcrum 


Pressure 


X 


Area 


X 


Distance   of  stem 
from  fulcrum 


weight  of  lever  X  distance  of 
its  center  of  gravity  from 
fulcrum 

weight  of  valve  and  stem  X 
distance  of  their  center  of 
gravity  from  the  fulcrum. 

In  order  to  find  one  of  these  qualities  we  must  know 
all  the  rest,  and  consequently  since  the  missing  quantity 
can  be  but  on  one  side  of  the  equal  mark  we  can  figure 
the  combined  value  of  the  quantities  on  one  side  of  the 


104 


BOILERS 


equation  (that  is,  in  one  set  of  brackets).  Then  we  can 
work  out  the  operation  indicated  on  the  other  side  as 
far  as  we  can  go.  If  the  missing  quantity  is  on  the 
left-hand  side  of  the  equation  it  can  be  found  by  divi- 
ding the  value  of  the  other  side  of  the  equation  by  the 
product  of  the  two  known  factors  on  the  left-hand  side. 

To  find  the  pressure  at  which  a  certain  valve  will 
blow  off: 

Multiply  the  weight  of  the  ball,  of  the  valve  and  stem 
and  of  the  lever,  each  by  the  distance  of  its  center  of  gravity 
from  the  fulcrum  and  add  the  products.  Multiply  the  area 
of  the  valve  by  the  distance  of  its  center  from  the  fulcrum 
and  divide  the  sum  above  found  by  the  product.  The 
quotient  will  be  the  pressure  required. 

Or  more  briefly: 

Divide  the  sum  of  the  moments  of  the  valve,  lever  and 
ball  by  the  product  of  the  area  of  the  valve  and  distance 
from  the  fulcrum. 

EXAMPLE. — At  what  pressure  will  a  3-inch  valve  blow 
off  with  stem  2\  inches  from  the  fulcrum,  valve  and  stem 
weighing  i  J  pounds,  lever  weighing  6  pounds,  having  its 
center  of  gravity  1 5  inches  from  the  fulcrum  and  weighted 
with  a  48-pound  ball  24  inches  from  the  fulcrum? 


Pressure 

X 
Area  =  7.0686 

X 

Distance  2j 
Product  =  15.90435  j 


48  X'24  =  1 1 52 
6x15=      90 
i.5X2i=         3.375 
Sum  of  moments  =  1245.375 


1 245-375  -  i5-90435  =  78-3  pounds. 


THE  SAFETY  VALVE  105 

This  is  all  that  we  shall  be  likely  to  wish  to  find  on 
this  side  of  the  equation,  for  the  distance  of  stem  is 
fixed  and  the  area  determined  by  other  considera- 
tions. 

The  other  two  things  that  interest  us  are  the  weight 
of  the  ball  and  its  distance  from  the  fulcrum. 

To  find  weight  of  ball  or  its  distance  from  fulcrum : 

Multiply  the  pressure  by  the  area  and  by  the  distance 
of  the  stem  from  the  fulcrum.  The  product  is  the 
moment  of  the  force. 

Multiply  the  weight  of  the  valve  by  the  distance  of  the 
stem  from  the  fulcrum;  multiply  the  weight  of  the  lever 
by  the  distance  of  its  center  of  gravity  from  the  fulcrum, 
and  add  the  products. 

Subtract  'the  sum  of  the  products  just  found  from  the 
moment  of  the  force,  and  the  difference  is  the  moment  of 
the  ball. 

Divide  the  moment  of  the  ball  by  the  weight  of  the 
ball  and  the  quotient  is  its  distance  from  the  fulcrum. 

Divide  the  moment  of  the  ball  by  the  distance  from  the 
fulcrum  and  the  quotient  is  the  weight  of  ball  required. 

EXAMPLE  —  What  weight  of  ball  at  the  same  dis- 
tance would  be  required  to  allow  the  valve  given  in 
the  previous  example  to  blow  at  75  pounds,  and  at 
what  distance  would  the  48-pound  ball  there  given 
have  to  be  placed  from  the  fulcrum  to  produce  the 
same  result? 


io6 


BOILERS 


Moment 


75 
X 

7.0686 
X 
21 


of  force  1 192.826 
93-375 

1099.451  mo- 
rn e  n  t  of 
ball 


Weight  X  distance  of  ball 

+ 
6X15        -  90.000 

+ 
1.5  X    2.25  =     3.375 

93.375  sum 
of  moments, 
valve  and 
lever. 


=  inches,  distance  of  ball. 
4b 

1099.451  .  . 

-  =  pounds,  weight  of  ball. 
24 

But  the  ideal  valve  should  stay  on  its  seat  until  the 
pressure  reaches  the  desired  limit,  then  open  wide  and 
discharge  the  excess.  This  result  is  accomplished  by  the 
construction  shown  in  Fig.  70.  With  the  first  opening 
of  the  valve  the  steam  passes  into  the  little  "huddling 
chamber"  made  by  the  cavity  near  the  overhanging 
edge  of  the  valve  and  a  similar  cavity  surrounding  the 
seat.  The  pressure  which  accumulates  here,  acting 
on  the  additional  area  of  the  valve,  raises  it  sharply 
with  the  "pop"  which  gives  the  valve  its  name,  and 
it  is  sustained  by  the  impact  and  reaction  of  the  issuing 
steam  until  the  pressure  has  subsided  sufficiently  to 
allow  the  spring  to  overcome  these  actions. 

The  outside  edge  of  the  lower  trough  in  the  valve 
shown  is  composed  of  an  adjustable  ring  which  may  be 


THE  SAFETY  VALVE 


107 


FIG.  70. 


io8  BOILERS 

screwed  up  or  down  so  as  to  diminish  or  increase  the  dis- 
tance between  the  overhanging  lip  of  the  valve  and  its 
own  inner  edge,  controlling  the  outlet  from  the  chamber; 
and  diminution  of  pressure  or  the  "blow  back"  required 
to  allow  the  valve  to  seat  so  that  the  valve  opens  wide 
at  a  given  pressure  and  seats  promptly  without  sizzling 
or  chattering  when  the  pressure  has  been  reduced  a  cer- 
tain amount  depending  upon  the  adjustment  of  the 
ring.  The  various  makers  have  adopted  different 
devices  for  adjusting  the  ring  or  other  device  for  con- 
trolling the  outflow  from  the  huddling  chamber. 

THE  CAPACITY  OF  SAFETY  VALVES 

Let  us  next  consider  the  capacity  of  valves;  how  large 
a  valve  is  required  for  a  given  boiler.  Most  of  the  rules 
deal  with  grate  surface  and  the  area  of  the  valve;  the 
rule  adopted  by  the  U.  S.  Board  of  Supervising  In- 
spectors being  one  square  inch  of  valve  area  for  each 
two  feet  of  grate  area.  That  the  valve  should  be  pro- 
portioned to  the  grate  surface  seems  proper  because 
it  is  the  grate  surface,  and  not  the  heating  surface, 
which  determines  and  limits  the  capacity  of  a  boiler. 
To  a  given  grate  surface,  however,  we  should  apportion 
a  sufficient  amount  of  area  of  opening,  and  this  area 
of  opening  is  not  proportional  to  the  area  of  the  valve 
but  to  the  diameter  and  lift.  A  valve  i  inch  in  diameter 
has  an  area  of  0.7854  of  a  square  inch,  but  that  does  not 
mean  that  there  will  be  an  opening  of  0.7854  of  a  square 
inch  for  the  steam  to  escape.  If  the  valve  is  flat,  as  in 
Fig.  71,  the  area  opened  for  the  discharge  of  steam 


THE  SAFETY   VALVE  109 

will  be  the  circumference  of  the  valve  multiplied  by 
the  lift.    The  circumference  is 

Diameter  X  3.1416  (i) 

and  the  area  of  the  complete  circle  is 

^.  ,.      Diameter 

Diameter  X  3.1416  X  -  (2) 

4 

and  the  area  for  the  escape  of  steam  is 

Diameter  X  3.1416  X  Lift.  (3) 

When  the  lift  is  one-quarter  the  diameter,  or 
Diameter 


the  area  for  the  escape  of  steam  is  the  same  as  the  area 
of  the  circle;  formula  3  is  the  same  as  formula  2. 


FIG.  71. 

When  a  flat  valve  has  lifted  a  quarter  of  its  diameter 
it  has  reached  the  limit  of  its  capacity  to  discharge 
steam.  It  doesn't  do  any  good  to  lift  higher,  for  the 
area  around  the  edge  of  the  valve  is  already  as  large  as 
the  area  of  the  valve  itself  and  the  capacity  of  the  valve 
is  proportional  to  the  area  or  the  square  of  the  diameter. 


no  BOILERS 

In  practice,  however,  the  lift  of  valves  is  much  less  than 
one-quarter  of  their  diameter,  and  for  a  given  lift  the 
area  for  the  escape  of  steam  is  proportional  to  the  cir- 
cumference or  the  diameter  rather  than  to  the  area. 
Most  of  the  rules,  however,  as  above  stated,  allow  a  given 
amount  of  valve  area  to  a  square  foot  of  grate  surface, 
and  make  the  allowance  liberal  enough  to  include  all 
conditions.  For  instance,  the  rule  of  the  U.  S.  Board  of 
Supervising  Inspectors  calls  for  one-half  a  square  inch 
of  valve  area  for  each  square  foot  of  grate  surface.  A 
4-inch  valve  has  about  12  square  inches  of  area  and 
would  thus  take  care  of  24  square  feet  of  grate.  It 
would  not  be  possible  to  burn  over  25  pounds  of  coal 
per  square  foot  of  grate  per  hour  with  natural  draft, 
nor  to  evaporate  over  12  pounds  of  water  with  a  pound 
of  coal,  so  that  the  boiler  could  not  possibly  make  more 
than 

25  X  12  X  24  =  7200  pounds  of  steam  per  hour, 
or 
7200  -T-  (60  X  60)  =  2  pounds  of  steam  per  second. 

Now  the  weight  of  the  steam  which  will  escape  through 
a  given  aperture  per  second  is  given  by  the  following 

f°rmUla:  wt        P^ssure  X  Area 

70 

that  is,  the  weight  in  pounds  which  will  escape  in  a 
second  is  equal  to  the  absolute  pressure  in  pounds  per 
square  inch  multiplied  by  the  area  in  square  inches  and 
divided  by  70. 


THE  SAFETY  VALVE  in 

On  the  other  hand,  the  area  required  to  discharge  a 
given  weight  is  Wd  h 

Area  =  -  — — 

Pressure 

that  is,  the  weight  in  pounds  to  be  discharged  per 
second  multiplied  by  70,  and  divided  by  the  absolute 
pressure  equals  the  required  area.  Now  we  have  found 
that  with  a  rate  of  combustion  practically  impossible, 
with  natural  draft,  and  a  practically  unattainable 
evaporation  per  pound  of  coal,  the  most  steam  that  the 
boiler  with  24  square  feet  of  grate  suface  could  furnish 
is  2  pounds  per  second.  The  area  required  to  discharge 
this  at  70  pounds  pressure,  absolute,  is 

2  X  7O 

— —  =  2  square  inches. 
70 

The  4-inch  valve  which  this  boiler  would  require 
would  have  a  circumference  of  practically  12  inches, 
and  would  need  to  lift  only  one-sixth  of  an  inch  to 
furnish  the  two  square  inches  of  opening  necessary 
to  discharge  the  steam,  for 

12  X  J  =  2. 

One-sixth  of  an  inch  is  only  one  twenty-fourth  of 
the  diameter  of  the  valve.  You  see  that  this  simple  rule 
gives  an  ample  margin,  requiring  but  a  small  lift  to 
discharge  more  steam  than  the  boiler  can  possibly  make. 
It  is  altogether  useless  and  nonsensical  to  figure  the 
areas  of  opening  to  four  places  of  decimals  involving 
with  beveled  seats  complicated  operations  with  sines 
and  cosines,  in  a  calculation  which  involves  no  accuracy 


112  BOILERS 

but  which  requires  simply  a  result  which  shall  be  amply 
large  to  cover  any  emergency  likely  to  be  encountered 
in  practice.  It  is  like  trying  to  measure  the  distance 
to  the  next  town  in  feet  and  inches,  in  order  to  answer 
a  man  who  would  be  abundantly  satisfied  to  know  that 
it  was  about  three-quarters  of  a  mile.  You  may  be 
sure  that  a  valve  which  has  a  square  inch  of  area  for 
each  two  square  feet  of  grate  surface  will  liberate  all  the 
steam  that  can  be  made  by  the  coal  that  you  can  burn 
on  that  grate  surface,  so  long  as  the  valve  is  free  and 
in  good  condition.  It  is  quite  probable  that  a  smaller 
valve  would  do,  but  in  a  matter  of  this  kind  we  want 
to  provide  not  the  smallest  that  will  possibly  do  but 
enough  capacity  to  be  absolutely  safe.  For  all  purposes 
of  ordinary  practice,  therefore,  divide  the  grate  surface 
by  2,  which  will  give  you  the  valve  area  required  and 
you  can  find  the  corresponding  diameter  by  multiply- 
ing the  square  root  of  the  area  by  1.128.  Don't  carry 
your  decimals  out  too  far  because  you  will  have  to  take 
the  nearest  commercial  size  after  all. 

Here  is  a  rule  which  will  give  you  the  diameter  of 
the  valve  in  inches  at  once: 

Multiply  the  square  root  of  the  grate  surface  by  0.8. 

This  would  be  particularly  handy  when  the  grate  is 
square,  or  nearly  so,  for  then  the  length  would  be  the 
square  root  of  the  area. 

You  can  see  how  the  rule  is  made,  or  rather,  makes 
itself. 

By  the  supervising  inspector's  rule  the  valve  area 
required  equals  the  grate  surface  divided  by  2. 


THE  SAFETY  VALVE  113 

A            grate  surface 
Area  - — . 

The  diameter  is  the  square  root  of  the  quotient  of 
the  area  divided  by  0.7854. 


TV  ,  /    area 

Diameter  = 


0.7854* 

And  since  in  this  case  the  area  equals  one-half  the  grate 
surface  the  diameter  will  be  the  square  root  of  one-half 
the  grate  surface  divided  by  0.7854. 


.  /grate  surface. 
Diameter  =  \/  -          —5 — 

V   2  x  0.7854 

Diameter  =  ./grate  surface 
V        1.5708 

We  can  get  rid  of  the  square  root  in  the  denominator 
by  finding  it  once  for  all.  It  is  1.25  very  nearly.  So 
our  formula  becomes 

TV  Vgrate  surface 

Diameter  =  -  — 

1.25 

Dividing  by  1.25  is  just  the  same  as  multiplying  by 
T.^y,  and  as  Tis  =  0.8,  the  multiplication  is  easier,  so 

we  have  / 

Diameter  =  V  grate  surface  X  0.8. 

The  grate  surface  will  never  be  so  large  that  the 
square  root  cannot  be  easily  determined  with  sufficient 
accuracy  mentally.  If  it  is  between  25  and  36  the  root 
is  between  5  and  6.  The  square  of  7  is  49,  of  8,  64,  etc., 
so  that  by  trial  the  root  can  be  determined  approxi- 


H4  BOILERS 

mately.  Here  is  an  easy  trick  to  get  the  square  of  a 
number  with  two  figures  ending  in  5 : 

Multiply  i  plus  the  left-hand  figure  by  the  left-hand 
figure,  and  annex  25  to  the  product. 

What  is  the  square  of  35? 

The  left-hand  figure  is  3.  Three  plus  i  is  4,  and  4  X 
3  =  12.  Annex  25  and  get  1225. 

This  rule  works  just  the  same  when  the  5  is  a  decimal, 
only  in  that  case  the  annexed  25  is  a  decimal  too,  and 
will  enable  you  to  determine  instantly  by  inspection 
the  nearest  number  advancing  by  halves  to  the  square 
root.  As  the  sizes  of  safety  valves  advance  by  half 
inches,  the  nearest  root  determined  in  this  way  will  be 
sufficiently  accurate,  as  we  have  to  take  the  nearest 
commercial  size  anyhow. 

What  is  the  square  of  6.5? 

Six  plus  i  =  7;  7  X  6  =  42;  add  25,  which  in  this 
case  will  be  a  decimal  fraction,  there  being  two  places 
to  point  off,  and  get  42.25. 

In  this  way  you  can  square  1.5,  2.5,  3.5,  etc.,  and 
this  is  as  near  as  it  is  ever  necessary  to  get  a  root  in  the 
above  formula.  Suppose,  for  instance,  you  had  58 
square  feet  of  grate  surface.  What  is  the  square  root? 
Seven  times  7  =  49,  and  8  X  8  =  64.  It  must  be 
between  7  and  8;  7.5  X  7.5  =  56.25. 

That  is  near  enough  to  58.  The  square  root  of  58 
is  really  7.61 5.  Multiplying  this  by  0.8  we  get  7.61 5  X 
0.8  =  6.092,  which  is  practically  a  6-inch  valve.  We 
should  have  got  at  the  same  result  if  we  had  taken  the 
square  root  as  7.5,  for  7.5  X  0.8  =  6. 

When  the  grate  surface  is  over  30  or  40  feet  it  is 


THE   SAFETY  VALVE  115 

better  to  get  the  required  capacity  by  putting  on  two 
valves  than  by  using  one  large  one.  In  fact  it  is  a 
pretty  good  plan  to  have  two  safety  valves  anyway. 
There  is  a  great  deal  of  responsibility  on  that  little 
appliance,  and  many  of  the  most  destructive  of  boiler 
explosions  would  have  been  avoided  by  an  operative 
safety  valve  of  sufficient  capacity.  So  many  little 
things  can  occur  to  make  it  hold  against  a  destructive 
pressure,  even  when  the  attendant  follows  the  usual 
directions  to  raise  it  from  its  seat  daily,  that  prudence 
dictates  the  use  of  an  auxiliary  valve.  It  would  be  a 
remarkable  coincidence  if  both  stuck  at  the  same  time 
without  criminal  negligence. 

The  amount  of  opening  of  an  ordinary  lever  safety 
valve  is  determined  by  the  amount  of  surplus  steam 
to  be  delivered.  If  the  boiler  is  making  more  steam 
than  is  to  be  taken  out  of  it  the  pressure  will  increase, 
and  when  it  reaches  an  amount  sufficient  to  overcome 
the  weight  of  the  ball,  etc.,  the  valve  will  be  raised 
a  little  from  its  seat  and  the  steam  will  escape.  If  the 
opening  thus  afforded  is  sufficient  with  the  other  drafts 
on  the  boiler  (such  as  the  supply  to  the  engine,  etc.) 
to  allow  all  the  steam  the  boiler  is  making  to  escape, 
the  valve  will  not  open  any  wider,  but  if  not  the  pressure 
will  continue  to  increase  and  force  the  valve  open 
until  the  steam  can  escape  as  fast  as  it  is  made.  As 
the  surplus  production  of  steam  decreases,  as  by  closing 
the  dampers  or  a  greater  demand  by  the  engine,  the 
valve  gradually  settles  down  to  its  seat  again. 

On  account  of  its  greater  lift  and  effective  discharging 
area  the  pop  valve  is  allowed  by  the  Board  of  Super- 


Ii6  BOILERS 

vising  Inspectors  three  square  feet  of  grate  surface 
per  inch  of  area  instead  of  two,  as  with  the  ordinary 
lever  valve. 

We  have  seen  that  the  escape  of  steam  through  an 
opening  of  given  size  is  proportional  to  the  absolute 
pressure.  Twice  as  much  steam  will  go  out  of  an  inch 
hole  in  a  minute  with  190  pounds  behind  it  as  with 
95  pounds.  It  is  presumed,  for  this  reason,  that  the 
inspectors  only  require  a  square  inch  of  valve  area  for 
every  6  feet  of  grate  surface  on  boilers  carrying  a  steam 
pressure  exceeding  175  pounds  gage. 

It  has  been  said  that  although  the  area  effective  for 
the  escape  of  steam  is  not  proportional  to  the  area  due 
to  the  diameter  of  the  valve,  and  although  the  latter 
area  is  that  used  in  the  formula  for  capacity,  the  allow- 
ance is  so  liberal  that  it  is  practically  useless  to  figure 
the  former.  It  may  be  interesting,  however,  to  know 
how  to  figure  it,  and  a  treatise  on  the  safety  valve 
would  hardly  be  complete  without  directions  for  so 
doing. 

With  a  flat  valve  we  have  already  seen  that  the  area 
for  the  escape  of  steam  is  the  lift  of  the  valve. multiplied 
by  its  circumference.  With  a  bevel-seated  valve  in 
which  the  valve  does  not  lift  out  of  the  seat  the  area 
A  A,  Fig.  72,  is  that  of  a  frustum  of  a  cone,  Fig.  73. 
Now  to  find  this  area  the  rule  is  to  add  the  circumfer- 
ence of  the  greater  circle  to  the  circumference  of  the 
lesser  CD;  divide  by  2,  and  multiply  by  the  slant  hight 
C  A.  In  other  words,  to  multiply  the  average  length 
of  the  strip  which  would  be  made  by  flattening  this 
surface  out  by  the  width  of  that  strip.  To  work  this 


THE  SAFETY  VALVE 


117 


rule  out  would  take  us  too  far  into  trigonometry,  but 
the  rule  follows: 

(i)    Multiply  the  diameter  of  the  valve  by  the  lift,  by 
the  stine  of  the  angle  of  inclination  and  by  3.1416. 


FIG.  72. 

(2)  Multiply  the  square  of  the  lift  by  the  square  of 
the  sine  of  the  angle  of  inclination,  by  the  cosine  of  this 
angle  and  by  3.1416. 

(3)  Add  these  two  products. 


The  U.  S.  rules  require  a  bevel  of  45  degrees,  and 
most  valves  are  made  with  seats  of  that  degree  of  in- 
clination. For  such  a  valve  the  rule  becomes: 

(i)  Multiply  the  diameter  of  the  valve  by  the  lift  and 
by  2.22. 


n8  BOILERS 

(2)  Multiply  the  square  oj  ihe  lift  by  i .  1 1 . 

(3)  Add  these  two  products. 

When  a  valve  with  a  beveled  seat  lifts  clear  of  the 
seat  as  a  valve  with  a  slight  bevel  may,  the  area  of 
the  opening  is  computed  by  the  above  rule  for  a  lift 
which  would  raise  it  to  the  upper  level  of  the  seat,  and 
to  this  is  added  the  circumference  of  the  valve  multi- 
plied by  the  lift  above  the  seat  level. 


THE   SAFETY   VALVE 


119 


2 

3 

4 

1,1 

3    > 

Area 
of 
Valve 

Weight  of  Valve 

and  Stem 

Pressure  Required  to 
Valve  and  Stem 

Lift 

In. 

Sq.  In. 

Pounds 

Pounds  per 

Sq.  In 

I 

o.i  104 

0.125 

0.131 

I 

0.1963 

0.156 

O. 

<  4 

o-7947 

0.713 

a 

0.441 

8 

0.187 

0. 

23 

0.423 

c 

•521 

I 

0.7854 

•  0.187 

o. 

34 

0.238 

0.432 

i\ 

1.2272 

0.312 

0.60 

0.254 

0.488 

I  2 

1.76" 

i 

0-437 

0. 

75 

0.247 

C 

•424 

2 

3-M 

6 

0-542               i.. 

6a 

5 

0. 

)7 

0.172 

0 

40 

• 

C 

.308 

2* 

4.9087 

0.8395             2.75 

1.69 

0.171 

0.560 

0-344 

3 

7.o6£ 

16 

1-339               3-. 

o 

2. 

53 

0.189 

0 

40 

c 

•329 

3-V 

9.62 

i 

1.8                   4-' 

r,5 

2. 

io 

0.187 

o 

40 

I 

c 

.270 

4 

12.5666 

2-371               5-' 

.s 

4- 

t2 

0.189 

0.458 

0.327 

4* 

15.904 

I 

3-0                   6.' 

s 

5. 

[8 

0.189 

o 

.42, 

I 

c 

.326 

5 

19-635 

o 

4.125               9.' 

s 

6. 

4S 

0.210 

o 

49 

c 

•324 

6 

28.2744 

5.87              11-875 

8.62 

0.208 

o 

420 

0.305 

5 

6 

7 

8 

Distance  of  Center  of 
Weight  of  Lever              Gravity  from 
Fulcrum 

Pressure  Required 
to  Raise  Lever 

Pressure  Required 
to  Raise  Valve, 
Stem  and  Lever 

Pounds 

Inches 

Pounds  per  Sq.  In. 

Pounds  per  Sq.  In. 

0.125 

3-25 

5-89 

6.003 

0.140 

0.20      3.0 

6 

25 

2 

Ss 

8.49 

3-6^ 

47 

9-203 

0-343 

0.38    4.812 

9.0 

4.98 

10.32 

5-403 

10.841 

l.O 

0.48      7-75 

9 

o 

8 

32 

5-50 

8.5 

;» 

5-932 

1.125 

0.65      7.312 

8 

Si  2 

5 

5 

OS 

3-73 

5-9<: 

>4 

4.218 

0-875 

0.87      6.875 

IO 

125 

2.87 

3-63 

3-II7 

4-054 

2-5 

•2.O 

1.  12      I3-3I2 

14.56 

i  i 

so 

7 

37 

7-42 

2-43 

7-5' 

.2 

7-92 

2-738 

3-5 

3-562 

4-0      15-25 

16.37 

tS 

O 

5 

70 

5-59 

7.24 

s.o< 

)I 

6.15 

7-584 

4-75 

5-8i2 

6.0      18.625 

17-37 

10 

25 

6 

07 

6.35 

7.07 

6.8 

SO 

6.84 

7-399 

5-75 

8.25 

10.50    21.75 

19.0 

10 

25 

5-78 

6,52 

9.08 

5-967 

7.01 

9-350 

6.0 

12.875 

13.0      23.0 

22.  0 

23 

4 

7,S 

8.20 

8-75 

4-9< 

)0 

8.66 

9.077 

7-o 

13-125 

i8.o      22.125 

23.0 

26.75 

3-89 

6,33 

11.09 

4.079 

6.75 

11.416 

10.75 

18.25 

20.0        25.25 

25-5 

31 

25 

5 

S  i 

7.22 

10.62 

5-7' 

I 

7.72 

10.944 

15.0 

21.25 

32.0     27.5 

29.62 

37-25 

5-56 

6.36 

12.05 

5.768 

6.78 

12.355 

9 

10 

Length  of  Lever 

Distance  of  Stem  from 
Fulcrum 

Weight  of  Ball  Ordinarily 
Furnished 

Inches 

Inches 

Pounds 

6.31 

0.62 

1-56 

5-62 

12.5 

0-75 

o-75 

3-2 

2.0 

9-50 

18.0 

0-75 

c 

•75 

5-5 

2.6 

14-87 

18.0 

1.19 

1.0 

8.12 

4-8 

14.4 

17-625 

1.19 

] 

•25 

9.62 

I  l.O 

13-4 

20.25 

1.19 

] 

•37 

15.37 

14.0 

26.1           29.50 

23-0 

1.44 

I 

87 

1.687 

19.0 

30 

24.0 

30.0          33.0 

30.0 

1.87 

2 

i 

l 

] 

.687 

29.0 

45 

34-5 

37-12         35.0 

38-5 

1.87 

2-25 

2.312 

38.0 

63 

50-5 

43-i           38-3 

75 

38-5 

2.25 

s 

3 

2 

.312 

48.5 

ss 

67.0 

45-5           44-5 

46-5 

2-37 

2-75 

2-75 

70.0 

110 

86.5 

43.75         46.1 

25 

53-5 

2-5 

3 

o 

2 

•75 

83.0 

I 

40 

86.5 

49.87         51.5 

0 

62.5 

2-5 

2 

"> 

"4 

.0 

98.0 

I 

68 

103.0 

54-5           59-50 

74-5 

2.625 

3-50 

3-5 

139.0 

220 

139.0 

X 

HORSE-POWER  OF   BOILERS1 

IN  a  recent  catalog  of  a  well-known  maker  of  engi- 
neering specialties  the  following  approximate  rules 
for  calculating  the  horse-power  of  various  kinds  of 
boilers  were  noticed  and  copied.  The  rules  are  in- 
tended for  use  in  determining  the  proper  sizes  of 
injectors  and  other  apparatus  when  the  exact  dimen- 
sions or  heating  surface  of  the  boiler  is  unknown  or 
hard  to  obtain: 

KIND  H.  P. 

Horizontal  Tubular  =  Dia.2  X  Length  -r-  5 

Vertical  Tubular  .  .  ==  Dia.2  X   Hight    -T-  4 

Flue  Boilers ==  Dia.  X  Length  H-  3 

Locomotive  Type  =  Dia.  of  Waist 2  X 

Length  over  all  -r-  6. 

All  dimensions  to  be  in  feet. 

In  the  first  and  third  cases  the  length  is  the  length 
of  the  tubes  or  that  of  a  "flush-head"  boiler  and  does 
not  include  the  extended  smoke-box.  In  the  second 
case,  the  hight  is  that  of  a  plain  vertical  boiler  in  which 
the  upper  part  of  the  tubes  is  above  the  water  line; 
it  is  not  the  hight  of  a  boiler  with  submerged  tubes. 

1  Contributed  to  Power  by  C.   G.   Robbins. 
120 


HORSE-POWER    OF   BOILERS  121 

The  extreme  simplicity  of  the  rules  aroused  curiosity 
as  to  their  accuracy,  and  comparisons  were  made 
between  manufacturers'  ratings  and  ratings  calculated 
by  the  formulas  above.  The  results  are  given  in  the 
accompanying  table.  They  agree  very  closely,  except 
in  a  few  of  the  larger  sizes  of  tubular  boilers,  where  the 
calculated  rating  falls  below  that  of  the  manufacturer. 
And  in  these  sizes  it  will  be  noticed  that  the  heating 
surface  per  horse-power  is  less  than  in  the  smaller  sizes 
where  the  two  ratings  practically  agree. 

It  is  quite  possible  that  the  ratings  of  other  manu- 
facturers would  show  a  better  or  worse  agreement. 
In  any  event,  the  rules  prove  to  be  valuable  for  just 
what  is  intended  and  will  save  considerable  trouble  in 
measuring  up  and  calculating  the  power  of  existing 
boilers  when  ordering  injectors,  feed  pumps,  and  the 
like. 


122 


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Diameter  (inches)  X  Length  (feet)  
Heating  Surface  
Manufacturers'  Rating  
Rating  bv  Rule  

K 

Diameter  (inches)  X  Length  (feet)  
Heating  Surface  
Manufacturers'  Rating  
Rating  bv  Rule  

Diameter  (inches)  X  Hight  (feet)  
Heating  Surface  
Manufacturers'  Rating  -  
Rating  bv  Rule  

Diameter  (inches)  X  Length  (feet)  
Heating  Surface  
Manufacturers'  Rating  
Rating  by  Rule  

Waist  Diam.  (in.)X  Length  (ft.)  J4oX 
Heating  Surface  26 
Manufacturers'  Rating  2 
Rating  by  Rule  2  s 

XI 


BOILER  APPLIANCES  AND  THEIR 
INSTALLATION      . 

IN  this  paper  it  is  my  aim  to  briefly  point  out  a  few 
of  the  deficiencies  which  not  only  exist  in  so  many 
of  the  less  modern  plants  located  in  isolated  places, 
but  which  are  too  often  found  in  the  large  and  perhaps 
otherwise  well-equipped  plants. 

First  in  importance  is  the  safety  valve,  which  in 
some  instances  can  be  called  such  in  name  only,  for 
in  their  neglected  or  overloaded  condition  they  would 
not  in  any  sense  answer  the  purpose  for  which  they 
are  intended.  We  still  find  a  few  engineers  who  per- 
sistently stick  to  the  old-style  lever  and  weight  safety 
valve  —  for  what  reason,  we  cannot  say,  unless  it  is 
because  they  can  be  overloaded  more  easily  than  the 
more  modern  spring-loaded  pop  valve.  Certainly 
everything  else  is  in  favor  of  the  pop  valve,  especially 
in  the  hands  of  incompetent  persons,  for  the  most 
successful  design  of  any  steam  appliance  is  that  one 
which  is  absolutely  fool-proof.  From  the  fact  that 
they  can  be  locked  and  made  fool-proof,  that  they  are 
much  more  reliable  in  their  action  and  so  much  less 
wasteful  of  steam,  it  is  believed  they  will  soon  be 
used  universally,  and  that  the  lever  valve  will  be  a 

123 


124  BOILERS 

thing  of  the  past.  But  with  all  their  advantages  they 
will  not  relieve  the  boiler  of  over-pressure  unless 
properly  installed  and  kept  in  operative  condition. 
Boilers  have  been  seen  equipped  with  these  valves 
ample  in  size  to  take  care  of  all  the  steam  the  boiler 
could  generate,  and  then  the  discharge  opening  re- 
duced to  one-third  the  area  of  the  valve  and  piped  up 
through  the  roof.  Again,  as  many  as  four  72x18 
boilers  have  been  seen  all  equipped  with  4-inch  pop 
valves,  and  all  piped  to  blow  into  one  continuous  4-inch 
header,  which  extended  through  the  wall.  There  is  no 
serious  objection  to  piping  the  waste  steam  from  a 
safety  valve  out  of  the  building,  when  properly  done, 
but  the  better  plan  would  be  to  have  a  suitable  ven- 
tilator in  the  roof,  and  let  them  discharge  in  the 
building.  There  are,  however,  many  plants  where  this 
cannot  be  done.  If  the  waste  pipe  is  run  out  of  the 
building,  it  should  never  be  smaller  than  the  valve 
itself,  and  if  it  is  necessary  to  carry  it  any  great  dis- 
tance, 20  feet  or  more,  the  pipe  should  be  increased  one 
size  and  connected  up  with  as  few  turns  as  possible. 
It  is  also  a  very  dangerous  plan  to  run  a  waste  pipe 
direct  from  the  safety  valve  horizontally  some  dis- 
tance, and  then  run  a  vertical  pipe  up  through  the 
roof,  unless  the  pipe  is  properly  supported  to  not  only 
sustain  its  own  weight,  but  to  carry  the  downward 
thrust  due  to  the  reaction  of  the  steam,  which  would 
in  turn  throw  a  severe  strain  on  the  casing  of  the 
valve  and  the  flange  bolts.  The  amount  of  pressure 
so  exerted  is  of  course  a  matter  of  conjecture,  for  the 
full  boiler  pressure  could  hardly  be  expected  to  be 


BOILER   APPLIANCES  125 

realized  on  the  waste  pipe.  However,  serious  acci- 
dents are  known  to  have  happened  from  just  such 
construction,  therefore  they  are  not  mere  possibilities. 
It  is  also  quite  necessary  that  the  waste  pipe  be  sup- 
plied with  the  proper  opening  for  free  and  continuous 
draining,  and  not  depend  altogether  on  the  drip  open- 
ing on  the  valve  itself. 

Next  in  importance  to  the  safety  valve  is  the  water 
column  and  its  connections.  There  are  probably 
more  accidents  to  boilers  traceable  to  defective  water 
columns  than  to  any  other  one  cause.  On  a  recent 
visit  to  a  new  plant  where  three  150  horse-power 
boilers  were  being  installed,  the  water  columns  were 
found  piped  up  with  f-inch  pipe,  with  several  turns  in 
the  lower  connection  and  with  no  blow-off  pipe. 
With  some  feed  waters  this  would  probably  answer 
the  purpose,  but  water  used  for  boiler  purposes  is 
often  found  which  would  close  up  the  lower  connec- 
tion in  a  very  few  days'  run.  In  this  case,  as  in  many 
others,  the  boiler  makers  were  at  fault,  as  they  were 
furnishing  the  attachments.  Water  columns  should 
never  be  connected  up  with  pipes  smaller  than  ij 
inches,  and  in  general  practice  ij-inch  pipe  is  better, 
but  in  every  instance  the  lower  connection  should  be 
provided  with  a  f-inch  blow-off,  and  for  convenience 
should  be  piped  to  discharge  into  the  ash-pit.  This 
blow-off  may  be  provided  with  any  good  valve  or 
cock,  but  if  the  latter  is  used,  a  closed  end  wrench 
should  be  provided,  as  an  adjustable  wrench  is  too 
apt  to  be  carried  away  and  the  blowing  out  neglected. 
The  removable  disk  Y-valves  now  on  the  market  have 


126  BOILERS 

been  found  very  serviceable  and  reliable  for  boiler 
blow-offs,  and  no  doubt  they  would  be  equally  as  good 
for  water  columns.  There  is  quite  a  difference  of 
opinion  among  engineers  as  to  the  advisability  of 
placing  stop  valves  in  the  column  connection,  but 
there  is  no  real  good  reason  advanced  why  they  should 
be  so  equipped.  Many  plants  with  valves  in  both 
the  lower  and  upper  connections  are  found,  but 
it  is  not  a  misstatement  to  say  that  one-half  the 
lower  valves  can  be  found  in  an  inoperative  condition, 
owing  to  the  accumulation  of  scale  on  the  seat  and 
valve.  The  less  the  number  of  attachments  which 
may  prove  a  source  of  danger  the  better.  In  connec- 
ting up  water  columns  it  is  a  good  plan  to  use  crosses 
in  the  lower  connections,  plugging  the  unused  open- 
ings with  gun-metal  or  brass  plugs.  These  will  be 
found  very  convenient  for  removing  deposit  which 
may  accumulate  and  cannot  readily  be  blown  out. 
Water  columns  are  often  too  small  to  give  the  best 
results.  The  chamber  should  be  at  least  3  inches, 
and  preferably  4,  in  diameter,  internally. 

Ignorance  is  also  often  displayed  in  placing  water- 
columns.  A  column  placed  too  high  is  fully  as  danger- 
ous in  the  hands  of  some  men  as  one  placed  too  low. 
In  plants  with  the  columns  so  placed  it  has  been  ob- 
served that  when  the  water  was  just  visible  in  the 
bottom  of  the  glass  there  would  be  6  inches  of  water 
above  the  top  of  upper  row  of  tubes.  The  fireman, 
knowing  this  fact,  will  carry  the  water  low  in  the  glass, 
and  if  by  chance  the  water  should  disappear  from 
view  altogether,  he  will  tell  you  that  it  just  went  out 


BOILER   APPLIANCES  127 

of  sight,  and  will  then  proceed  to  speed  up  the  boiler 
feed  pump.  A  better  and  safer  plan  is  to  set  the 
column  with  the  bottom  of  the  glass  just  level  with  the 
top  of  the  upper  row  of  tubes,  then  pull  or  cover  the  fire 
before  the  water  leaves  the  glass,  in  case  of  the  failure 
of  the  water  supply.  Gage-glass  valves  and  try-cocks 
are  also  too  often  neglected.  While  it  is  believed  there 
is  no  better  way  of  ascertaining  the  hight  of  water  in 
boiler  than  by  blowing  out  the  water  column  and 
then  noting  the  rapidity  with  which  water  returns  to 
the  glass,  do  not  neglect  the  try-cocks,  for  the  water 
glasses  will  break  and  at  times  when  it  is  not  con- 
venient to  replace  them;  then  the  try-cocks  will  come 
in  handy,  and  should  be  found  in  working  order. 

The  steam  gage  is  next  in  importance,  but,  as  a  rule, 
receives  little  attention.  The  dial  on  the  factory 
clock  is  kept  clean,  so  there  will  be  no  mistake  in  read- 
ing the  time  when  the  whistle  should  be  blown;  but 
with  the  gage  it  is  different;  it  has  no  such  important 
duties  to  perform.  A  steam  gage  is  not  the  delicate 
instrument  that  some  would  believe.  However,  their 
accuracy  is  easily  destroyed,  if  not  properly  connected 
up.  They  should  not  be  attached  to  the  breeching 
or  boiler  front,  unless  protected  from  the  heat,  and 
they  should  be  provided  with  a  water  trap  to  protect 
the  Bourdon  spring  from  the  heat  of  the  live  steam; 
otherwise  they  will  not  give  correct  readings,  and  may 
be  ruined  altogether.  The  best  form  of  trap  is  one 
made  up  of  nipples  and  fittings,  with  a  small  drain 
cock  placed  in  the  lowest  point  of  trap  for  the  pur- 
pose of  blowing  out  and  of  draining,  to  prevent  freez- 


128  BOILERS 

ing  in  winter.     A  trap  of  this  kind  will  be  found  much 
easier  to  clean,  in  case  of  stopping  up,  than  the  bent 

pipe. 

NOTES 

The  use  of  cast-iron  flanged  nozzles  connecting 
boilers  to  steam  pipes  is  being  superseded  by  dropped 
forge  steel  flanges.  The  former  are  objectionable, 
for  the  rivet  holes  must  be  accurately  drilled  and  the 
curve  must  be  a  neat  fit  to  the  boiler  plate  or  a  calking 
gasket  be  provided  to  make  the  joint  tight.  Then 
such  flanges  will  fail  by  fracture  in  riveting  after 
some  time  and  money  has  been  spent  on  the  job.  If 
the  cast  nozzle  is  flanged  to  receive  the  steam  pipe, 
the  holes  for  bolts  must  be  drilled  out  and  bolts  go 
with  the  nozzle.  Many  buyers  object  to  superfluous 
flanges  as  that  much  more  for  the  engineers  to  care  for 
and  pack.  Then  if  the  plant  be  a  one  or  two  boiler 
one  the  best  plan  is  to  have  no  flanges  between  the 
boiler  and  the  main  steam  valve,  for  if  a  flange  blows 
out  the  packing  one  can  readily  shut  the  main  steam 
valve  and  repack  it,  while  on  the  other  hand  one  will 
wait  until  the  boiler  cools  off.  With  regard  to  strength 
of  material,  while  cast  iron  can  be  made,  and  un- 
doubtedly is,  to  run  as  high  as  25,000  pounds  tensile 
strength,  the  fact  is  it  may  run  less  than  that,  and  in 
calculating  averages  must  be  taken,  which  doubtless 
will  not  exceed  15,000  pounds  per  square  inch.  In 
addition  allowance  must  be  made  for  shrinkage  strains 
in  such  castings;  usually  an  unknown  amount,  but 
allowance  should  be  given.  If  the  flange  be  threaded 
the  strength  of  such  threads  will  of  course  not  equal 


BOILER   APPLIANCES  129 

threads  in  forged  steel.  The  expansion  of  the  boiler 
shell  sets  up  strains  on  these  flanges,  and  while  cast 
iron  resists  bending  or  flexure  well,  that  is  of  no  special 
value,  as  the  strains  are  continuous  and  unavoidable. 
On  the  contrary  dropped  forged  steel  flanges  furnished 
in  all  pipe  sizes  and  to  fit  practically  any  required 
circle  are  now  made  and  kept  in  stock  by  boiler  supply 
houses,  ready  for  attaching  and  tapped  to  size. 

The  tensile  strength  equals  flange  steel.  Granting 
cast  iron  15,000  tensile  strength  and  forgings  60,000, 
note  the  wide  difference  in  strengthening  by  rein- 
forcement of  the  hole  cut  in  the  boiler  shell.  The 
steel  flange  may  have  rivet  holes  punched  to  within 
J-inch  of  size  and  reamed  out  without  damage.  It 
will  "give"  in  fitting  and  riveting  to  the  shell  and  no 
gasket  is  needed.  A  Fuller  calking  tool  will  quickly 
close  any  leak  at  the  seam,  but  such  rarely  occurs, 
as  it  is  forged  on  a  smooth  die.  The  threads  are  ij 
inches  deep  on  a  6-inch  size,  and  are  very  strong. 
From  all  of  the  above,  proved  by  experience,  the  steel 
flange  is  vastly  better  than  the  cast-iron  one.  Never- 
theless many  old  men  will  not  accept  anything  other 
than  the  latter,  doubtless  due  to  their  opinions  hav- 
ing formed  and  "froze  in"  years  ago. 

The  foregoing  applies  to  a  large  extent  to  cast-iron 
man-head  frames,  but  as  such  are  of  larger  size  it  is 
clear  that  the  strains  due  to  shrinkage  and  expansion 
under  working  pressure  must  be  kept  in  mind  as  the 
casting  is  narrower  at  the  cross-section  of  the  minor 
ellipse  than  at  major.  Presuming  the  casting  projects 
upward  and  inward  to  receive  the  plate,  the  usual 


130  BOILERS 

type,  it  is  likely  shrinkage  strains  occur  at  the  corners 
of  the  angles.  Considering  the  large  amount  of  the 
shell  cut  away  for  an  11X15  inch  man-head,  and  allow- 
ing 15,000  tensile  strength  for  castings,  it  is  often  the 
case  that  the  weakest  link  in  the  chain  composing  the 
strength  of  a  boiler  is  at  this  point.  In  my  opinion 
engineers,  designers  and  boiler  makers  should  abandon 
cast-iron  man-head  frames,  if  for  no  other  reason  than 
to  strengthen  the  boiler.  Such  frames  should  be,  as 
high-class  shops  now  use,  weldless  flange  steel,  forged 
into  shape  and  double-riveted  to  the  shell  plate.  No 
one  thus  far  has  seen  a  cast  man-head  frame  double- 
riveted  to  the  shell.  Please  note  that  point. 

With  an  elliptical  steel  frame  to  save  packing  and 
also  profanity,  a  J-inch  ring  should  be  shrunk  on 
to  the  inner  flange  and  planed  off  to  give  a  seat  one 
inch  wide.  But  if  packing  costs  money,  then  in  the 
man-head  plate  have  a  groove  provided  so  the  packing 
cannot  be  forced  out,  and  a  piece  of  asbestos  f  rope 
with  plumbago  and  oil  when  the  joint  is  opened  will 
last  two  years.  In  one  case  with  two  boilers  washed 
out  every  two  weeks  it  cost  $3.00  each  opening  for 
gaskets.  The  old  plates  were  on  my  advice  replaced 
with  new  ones  grooved  and  the  cost  for  gaskets  re- 
duced from  $78  per  annum  to  $2,  a  thrifty  saving  by 
the  way. 

Returning  to  the  strength  of  the  steel  frame,  it  is  so 
superior  to  the  cast  one  in  every  manner  that  no  com- 
parison can  be  made.  Nor  indeed  is  it  necessary  to 
buy  one  particular  type,  as  while  these  frames  are 
patented,  several  being  of  about  equal  merit,  prices 


BOILER   APPLIANCES  131 

are  not  kept  at  a  high  point.  In  view  of  the  failures 
in  riveting  castings  and  including  drilling  it  is  doubt- 
less true  the  steel  frames  like  the  steel  nozzles  are 
cheaper  to  the  builder,  while  in  every  way  each  should 
be  more  desirable  to  the  buyer,  the  engineer  and  the 
insurance  companies. 

To  a  large  extent  the  above  applies  with  equal  truth 
to  pressed  steel  lugs  or  brackets  supporting  the  boiler, 
but  in  addition  in  shipping  a  boiler,  while  a  steel  lug 
may  by  transit  be  bent,  it  can  easily  be  straightened 
and  without  injury  —  a  valuable  quality.  When  a 
boiler  is  set,  the  lugs  being  out  of  sight  are  out  of  mind. 
As  the  walls  transmit  heat  it  is  clear  the  lugs  become 
quite  warm,  for  it  is  usual  to  protect  them  by  the 
thickness  of  only  one  brick,  and  as  the  lug  is  covered 
outside,  the  heat  is  not  lost  but  retained.  More  pro- 
tection should  be  given  under  a  lug,  at  least  two  courses 
of  brick  and  an  air  space  be  open  above  the  lug. 

Reverting  to  strength,  note  that  it  is  usual  to  have 
a  space  of  4  inches  between  the  boiler  and  the  side 
wall,  and  by  properly  carrying  the  brick  out  to  the 
boiler  the  weight  is  transmitted  over  the  entire  seat  of 
the  hig.  On  the  other  hand,  if  this  is  not  done,  then 
one  must  make  the  lug  stronger  to  allow  for  the  4-inch 
span.  When  of  cast  iron,  we  cannot,  as  stated,  accept 
more  than  15,000  pounds  tensile  strength  per  square 
inch,  while  if  of  steel  we  can  take  60,000  tensile  strength 
as  the  ultimate  strength.  Hence  a  |-inch  steel  equals 
a  i -inch  casting;  but  the  lugs  are  made,  if  of  steel,  of 
equal  width  with  ordinary  cast-iron  lugs,  and  in  addi- 
tion the  pressed  ribs  make  it  much  wider.  It  is  usual 


132  BOILERS 

to  have  such  lugs  of  f-inch  plate,  equaling  castings  of 
i£  inches  in  strength.  Steel  lugs  are  easily  punched 
and  fitted  to  boiler  shells.  There  is  life  in  them,  as 
before  reaching  a  breaking  point  through  overload  the 
give  would  be  noticeable,  while  the  casting  would  fail 
without  warning. 

From  all  of  the  above  you  will  doubtless  agree  that 
in  the  modern  steam  boiler  steel  is  winning  its  fight 
over  cast  iron  through  its  superiority  in  strength  and 
its  adaptability  for  these  purposes.  In  the  up-to- 
date  shops  these  arguments  plus  actual  reduction  in 
costs  have  led  to  its  adoption. 


XII 


CARE  OF  THE   HORIZONTAL  TUBULAR 
BOILER1 

ALTHOUGH  the  boiler  room  is  the  very  heart  of  every 
steam  plant,  it  is  frequently  the  subject  of  the  grossest 
neglect,  and  the  instances  in  which  it  receives  the  care 
and  thought  to  which  it  is  entitled  are  very  rare. 
Under  the  very  best  of  conditions  it  is  wasteful,  but 
in  a  great  many,  in  fact  in  the  majority  of  cases,  it 
is  much  more  so  than  there  is  any  necessity  of.  It 
must  be  admitted  that  the  boiler  room  is  necessarily 
a  rather  dirty  and  uninviting  place,  but  that  is  no 
excuse  for  neglecting  it. 

In  the  engine  room  every  possible  economy  is  prac- 
tised. Every  foot  of  steam  pipe  is  covered;  the  best 
grade  of  oil  is  used;  the  engine  valves  are  set  with  the 
greatest  care;  belts  are  run  as  slack  as  possible;  and 
many  other  points  are  watched  in  order  to  keep  the 
steam  consumption  down  to  the  lowest  possible  point. 
This  is  all  very  proper  and  good,  and  should  be  en- 
couraged as  much  as  possible,  but  in  many  cases  far 
more  serious  losses  are  permitted  in  the  boiler  room, 
and  it  is  these  which  can  and  should  be  stopped. 

1  Contributed   to   Power  by   M.   Kennett. 
133 


134  BOILERS 

A  COMMON  SOURCE  OF  Loss 

A  very  common  source  of  loss  is  the  leakage  of  cold 
air  through  cracks  in  the  settings.  When  flat  plates 
from  one  side  wall  to  the  other  are  used  over  the  rear 
of  the  combustion  chamber,  it  is  not  unusual  to  find 
a  space  of  from  J  to  i  inch  between  the  rear  boiler 
head  and  the  plate.  This  admits  a  large  quantity 
of  cold  air  to  pass  directly  through  the  upper  tubes, 
which  are  the  most  valuable  for  generating  steam. 

As  a  rule  these  openings  are  not  caused  by  faulty 
setting  of  the  plate,  as  these  are  usually  well  set, 
making  a  tight  joint,  before  the  boiler  is  fired  up. 
But  when  the  boiler  becomes  heated  and  expands,  the 
plate  is  forced  back,  and  when  the  boiler  cools,  a  small 
space  is  left  between  it  and  the  plate.  Pieces  of  mortar 
and  chips  of  brick  lodge  here,  and  when  the  boiler  is 
again  fired  up  and  expands,  the  plate  is  forced  still 
farther  back.  It  is  practically  impossible  to  prevent 
these  openings  with  this  style  of  plate,  but  matters 
can  be  greatly  improved  by  packing  the  crack  loosely 
with  waste  which  has  been  filled  with  soft  fire-clay, 
as  this  forms  an  elastic  packing  which  will  not  readily 
burn  out. 

The  style  of  arch  shown  in  Fig.  74  is  practically  free 
from  this  objection  as  it  rests  against  the  boiler  head 
and  follows  its  movements.  This  plan  is  open  to  the 
objection  that  the  angle  iron  on  the  boiler  head  finally 
burns  out,  and  in  order  to  replace  it  the  studs  have  to 
be  removed  from  the  head,  and  new  ones  put  in,  with 
the  attendant  trouble  of  making  the  job  tight.  Bear- 


CARE  OF  THE  HORIZONTAL  TUBULAR   BOILER      135 

ing  bars  are  sometimes  built  into  the  side  walls  as  a 
substitute  for  these  angle  irons,  but  they  soon  burn 
out,  also.  All  trouble  from  this  source  may  be  over- 
come by  using  an  extra  heavy  pipe  as  a  bearing  bar, 
and  making  it  part  of  the  feed  line,  so  that  water  is 
being  constantly  pumped  through  it.  Or,  as  in  one 
case  in  mind,  a  small  open  tank  may  be  provided  for 
this  purpose,  the  water  circulating  by  gravity. 

Numerous  other  cracks  are  constantly  developing 
in  various  parts  of  the  settings,  and  should  be  kept 
well  filled  with  clay. 

The  combustion  chamber  back  of  the  bridgewall 
should  not  be  allowed  to  become  filled  with  ashes  to 
such  an  extent  as  to  impede  the  draft. 

PROPER  DEPTH  OF  COMBUSTION  CHAMBER 

There  is  a  great  difference  of  opinion  concerning  the 
proper  depth  of  this  chamber,  some  engineers  claiming 
that  it  should  be  filled  up  level  with  the  bridgewall, 
while  others  claim  it  should  be  quite  deep.  Much 
depends  upon  the  kind  of  fuel  used,  the  writer  believing 
that  when  soft  coal  is  used,  it  should  be  fairly  deep  to 
allow  the  unburned  gases  to  become  thoroughly 
mixed  with  the  air  and  burn.  An  excellent  plan  is  to 
slope  the  flame  bed  from  almost  the  hight  of  the  bridge- 
wall  to  the  ground  in  the  rear,  and  pave  it  with  fire- 
brick. This  brick  paving  becomes  incandescent  and 
ignites  the  gases  and  also  reflects  the  heat  upward  toward 
the  boiler.  This  style  of  chamber  is  easily  cleaned  out 
through  a  door  in  the  rear  wall  at  the  level  of  the  floor, 
and  the  ashes  should  be  raked  out  every  day. 


136 


BOILERS 


CARE   OF  THE  HORIZONTAL  TUBULAR  BOILER      137 

Do  not  make  the  mistake  of  placing  this  door  one 
or  two  feet  above  the  ground,  as  is  frequently  done, 
thus  making  it  necessary  to  enter  the  chamber  to  clean 
it. 

The  hight  and  form  of  the  bridgewall  are  also  worthy 
of  consideration.  The  principal  object  of  the  bridge- 
wall  is  to  keep  the  fire  on  the  grates,  and  it  should 
not  be  built  up  too  close  to  the  boiler,  nor  should  it 
be  curved  to  conform  to  the  circle  of  the  boiler  shell. 
Such  walls  tend  to  concentrate  the  intense  heat  in  the 
fire-box.  This  burns  out  the  fire-door  linings,  and 
increases  the  danger  of  burning  the  fire-sheet,  in  case 
scale  or  sediment  collects  on  it.  They  also  prevent 
the  free  passage  of  a  sufficient  quantity  of  air  into  the 
combustion  chamber  to  burn  the  gases. 

We  believe  that  all  bridgewalls  should  be  straight 
and  not  closer  to  the  shell  than  12  inches  for  48-inch 
boilers,  and  20  inches  for  y2-inch  boilers.  In  many 
cases  we  believe  these  distances  may  be  increased  with 
advantage. 

The  necessity  of  keeping  the  tubes  free  of  soot  is 
pretty  well  understood,  and  this  point  usually  receives 
proper  attention.  In  addition  to  the  usual  blowing 
out  with  the  steam  blower,  however,  they  should  be 
thoroughly  scraped  at  least  once  a  week.  The  steam 
from  the  blower  condenses  to  a  great  extent  before 
reaching  the  rear  end  of  the  tubes;  a  great  deal  of  the 
soot  is  simply  moistened  and  left  adhering  to  the 
tubes  and  soon  burns  into  a  hard  scale  which  can  only 
be  removed  by  a  thorough  scraping. 


138  BOILERS 

IMPORTANCE  OF  CLEANING  BOILERS 

Generally  speaking,  there  are  few  operations  about 
a  steam  plant  which  are  so  badly  neglected  as  the 
cleaning  of  the  boilers.  The  operation  too  often  con- 
sists simply  of  letting  the  water  out,  removing  the 
lower  man-head,  and  washing  the  mud  out  with  a  hose. 
The  natural  result  is  that  the  heating  surfaces,  espe- 
cially the  tubes,  become  heavily  coated  with  scale. 
This  accumulates  most  rapidly  at  the  rear  head,  and 
the  space  between  the  tubes  soon  becomes  entirely 
choked  for  a  short  distance,  preventing  the  free  access 
of  the  water  to  the  tube-sheet.  This  causes  the  tube 
ends  to  become  overheated  and  they  begin  to  leak. 
The  only  remedy  is  to  remove  the  scale  and  reroll  the 
tubes,  but  in  order  to  remove  the  scale  it  is  usually, 
or  at  least  frequently,  necessary  to  cut  out  some  of 
the  tubes. 

The  bagging  of  boilers  due  to  the  accumulation  of 
scale  and  dirt  is  of  such  common  occurrence  as  to  re- 
quire no  discussion,  other  than  to  say  that  it  is  the 
result  of  improper  cleaning. 

Of  course  there  are  many  cases  in  which, 'even  with 
the  best  possible  care,  a  great  deal  of  scale  will  form, 
or  where  it  is  impossible  to  keep  the  boiler  out  of  com- 
mission long  enough  to  clean  it  properly.  But  there 
are  also  many  cases  in  which  a  pretty  thorough  clean- 
ing could  be  given  if  the  engineer  really  wanted  it 
done,  and  realized  its  importance  sufficiently  to  see 
that  it  was  done. 

The  number  of  boiler  compounds  which  are  guar- 


CARE  OF  THE  HORIZONTAL  TUBULAR  BOILER       139 

anteed  to  keep  boilers  clean  is  legion,  but  still  it  will 
be  hard  to  find  the  one  which  will  remove  the  scale 
and  hand  it  to  the  engineer,  although  this  seems  to  be 
what  some  men  expect  of  it.  Most  of  them  will  do  all 
that  can  be  expected  of  them.  They  will  soften  and 
loosen  the  scale  and  considerable  of  it  will  drop  off. 
After  it  is  loosened  the  boiler  cleaner  should  scrape 
it  off  by  entering  the  top  and  bottom  with  suitable 
tools.  Boiler  compounds,  like  many  other  things, 
should  be  mixed  with  a  good  deal  of  common  sense,  then 
results  will  be  obtained.  When  a  boiler  is  badly  scaled 
great  care  must  be  exercised  in  the  use  of  a  scale  solvent, 
as  it  may  cause  considerable  scale  to  drop  off  and  bag 
a  sheet.  The  action  can  be  watched  by  frequent  clean- 
ings and,  if  there  seems  to  be  danger  of  such  trouble, 
more  frequent  cleaning  may  be  resorted  to,  or  less  sol- 
vent may  be  used. 

An  excellent  plan  is  to  use  a  scale  pan,  which  is  a 
shallow  pan  about  four  to  six  feet  long  and  as  wide  as 
can  be  passed  through  the  manhole.  It  is  supported 
by  light  legs  about  three  inches  long,  and  is  placed  on 
the  fire-sheet  directly  over  the  grates.  As  the  scale 
falls  it  is  caught  by  this  pan  and  is  thus  kept  off  the 
sheet,  preventing  the  bagging  of  the  latter. 

OIL  A  SOURCE  OF  DIFFICULTY 

Probably  the  most  difficult  thing  to  cope  with  in  a 
boiler  is  oil.  There  are  many  different  kinds  of  oil. 
Genuine  crude  petroleum  is  oil,  but  when  properly  used, 
it  is  difficult  to  find  anything  which  excels  it  for  keeping 
boilers  free  from  scale.  Kerosene  is  frequently  used 


140  BOILERS 

for  the  same  purpose,  and  neither  causes  any  trouble. 
The  oil  which  we  refer  to,  and  which  causes  the  most 
trouble,  is  the  cylinder-oil  carried  over  by  the  exhaust 
to  an  open  heater  or  hot-well,  and  from  thence  into  the 
boilers.  This  first  appears  at  about  the  water  line, 
and  on  the  top  tubes,  where  it  gives  no  trouble,  but 
it  soon  spreads  over  the  entire  heating  surface,  and  it 
is  surprising  how  little  it  takes  to  cause  a  very  serious 
bulge  on  a  fire-sheet. 

A  bulge  caused  by  oil  is  different  from  one  caused  by 
scale  or  mud  in  that  it  usually  covers  considerable 
area,  while  the  latter  is  not  often  over  a  foot  or  18  inches 
in  diameter,  but  is  much  deeper  in  proportion  to  its  size. 
When  a  bulge  is  from  three  to  five  feet  long,  as  those 
caused  by  oil  usually  are,  there  is  nothing  to  be  done 
but  to  put  in  a  new  sheet.  This  is  an  expensive  repair, 
as  it  necessitates  tearing  down  the  brickwork  in  addi- 
tion to  the  boiler  work. 

The  best  method  of  removing  the  oil  from  the  feed- 
water  is  to  filter  it  through  a  bed  of  coke  and  excelsior. 
This  must  be  renewed  from  time  to  time,  as  it  soon  gets 
coated  with  the  oil  and  becomes  useless.  .  There  are 
numerous  separators  on  the  market  guaranteed  to  ex- 
tract the  oil  from  the  steam  and  water,  but  invariably 
better  results  have  been  obtained  from  the  filter. 

FAULTY  BLOW-OFF  PIPES 

The  records  of  a  large  boiler-insurance  company 
show  that  there  are  more  claims  due  to  the  failure  of 
blow-off  pipes  than  from  any  other  single  cause.  A 
volume  might  be  written  on  this,  for  the  blow-off  pipe 


CARE   OF   THE  HORIZONTAL  TUBULAR   BOILER      141 

certainly  is  a  very  troublesome,  although  necessary 
evil.  When  the  feed-water  is  not  introduced  through 
the  blow-off  pipe,  there  is  practically  no  circulation  in 
it,  and  mud  and  sediment  are  very  apt  to  collect.  If 
the  pipe  is  not  protected  from  the  direct  action  of  the 
fire,  this  is  very  liable  to  cause  it  to  burn  and  burst. 
Even  though  this  results  in  no  damage,  it  necessitates 
cutting  out  the  boiler,  and  this  may  happen  at  a  very 
inopportune  time.  If,  however,  the  boiler  is  fed  through 
the  blow-off,  the  danger  of  such  accident  is  reduced 
to  the  minimum,  but  even  then  it  is  better  to  protect 
the  pipe  from  the  direct  action  of  the  flame  and  gases. 

It  is  a  very  common  practice  to  incase  the  pipe  in  a 
sleeve  formed  of  a  pipe  one  or  two  sizes  larger.  This 
is  of  no  value  unless  the  sleeve  is  arranged  as  in  Fig.  75, 
so  as  to  allow  a  circulation  of  air  between  it  and  the 
blow-off  pipe.  When  the  sleeve  is  simply  slipped  over 
the  pipe  and  allowed  to  hang  loose,  as  in  Fig.  76,  it  is 
of  no  value  whatever. 

In  order  to  make  it  effective,  the  sleeve  should  in- 
close the  entire  pipe  from  the  outside  of  the  setting  to 
within  an  inch  or  so  from  the  boiler,  and  should  be  held 
in  position  by  iron  wedges,  as  shown  in  Fig.  75.  This 
allows  the  cool  air  to  traverse  the  entire  pipe,  being 
drawn  in  by  the  draft.  While  this  is  an  excellent  plan 
theoretically,  it  is  open  to  the  very  serious  objection 
that  the  sleeve  rapidly  burns  out,  and  in  order  to 
renew  it,  the  entire  blow-off  pipe  has  to  be  taken  down. 
There  is  a  cast-iron  split  sleeve  made  for  this  purpose, 
which  can  be  replaced  at  any  time  without  disturbing 
the  pipe. 


I42  BOILERS 

Perhaps  as  good  a  plan  as  any,  all  things  considered, 
is  to  run  the  blow-off  pipe  straight  down  to  the  bottom 
of  the  combustion  chamber  and  build  a  V-shaped 
fire-brick  pier  in  front  of  it,  just  far  enough  away  to 
allow  removing  the  pipe  and  replacing  it  without  dis- 
turbing the  pier. 

When  necessary  to  use  fittings  in  the  combustion 
chamber,  they  should  be  of  either  cast  steel  or  malleable 
iron,  as  cast  iron  is  too  liable  to  crack  when  exposed 
to  high  temperature. 

BEST  METHOD  OF  FEEDING  A  BOILER 

The  method  of  feeding  boilers  has  had  a  great  deal 
of  discussion,  some  advocating  feeding  through  the 
blow-off,  and  some  as  strongly  advising  the  top  feed 
with  a  certain  type  of  heater,  the  water  passing  through 
a  length  of  pipe  in  the  steam  space  of  the  boiler,  and 
thus  becoming  heated  to  more  nearly  the  temperature 
of  the  water  in  the  boiler  before  discharging. 

It  is  the  general  opinion  the  top  feed  is,  generally 
speaking,  the  proper  method;  but  circumstances  must 
necessarily  determine  the  best  method  for  each  par- 
ticular case,  and  the  writer  has  seen  many  cases  where 
he  has  advised  feeding  through  the  blow-off.  The 
objection  to  this  method  is  that  the  comparatively  cool 
water  from  the  heater  is  discharged  on  the  hot  sheets. 
The  water  from  the  heater  is  hot,  it  is  true,  but  when 
compared  to  that  in  the  boiler  there  is  considerable 
difference  in  temperature.  It  is  seldom  that  the  ordi- 
nary exhaust  heater,  except  the  most  modern  open 
heaters,  raises  the  water  to  more  than  175  degrees, 


CARE   OF  THE  HORIZONTAL  TUBULAR   BOILER      143 

while  the  temperature  of  the  water  in  the  boiler  at  100 
pounds  pressure  is  337  degrees.  This  is  a  difference 
of  162  degrees,  or  about  the  same  difference  as  between 
boiling  water  and  a  block  of  ice.  Now  if  this  water  is 
passed  through  twelve  or  fourteen  feet  of  pipe  in  the 
steam  space  before  it  is  discharged,  its  temperature 
will  be  raised,  perhaps  not  very  much,  but  at  the  end 
of  this  pipe  it  is  discharged  in  the  body  of  water  in  the 
boiler,  and  cannot  come  in  contact  with  the  sheets 
until  it  has  mingled  with  and  attained  the  temperature 
of  this  water.  If  an  injection  is  used,  or  if  there  is  no 
heater  used  in  connection  with  the  feed-pump,  the  top 
feed  should  be  used  by  all  means. 

It  is  fully  realized  that  with  some  waters  this  internal 
pipe  soon  chokes  up,  especially  at  the  end,  but  usually 
this  is  readily  cleaned,  when  the  boiler  is  cleaned,  and 
it  may  easily  be  made  .of  sufficient  area  to  run  three  or 
four  weeks  without  giving  any  trouble. 

The  point  of  discharge  for  this  pipe  is  largely  a  matter 
of  personal  preference,  but  it  should  be  remembered 
that  the  sediment  will  collect  worst  at  the  point  of 
discharge.  A  good  plan  is  to  have  the  pipe  enter  the 
front  head  just  above  the  tubes  and  at  one  side  of 
the  boiler,  carrying  it  to  within  two  or  three  feet  of 
the  back  head,  and  supporting  it  by  brackets  from  the 
braces.  From  here  let  it  run  across  to  the  middle  space 
between  the  tubes,  using  a  union  near  the  end  of  this 
piece.  Then  drop  two  pipes  between  these  tubes  to  the 
level  of  the  lower  tubes.  This  makes  it  very  easy  to 
clean  these  down  pipes,  by  opening  the  union  and 
removing  them. 


144  BOILERS 

If  there  is  no  manhole  below  the  tubes,  so  that  the 
scale  and  sediment  cannot  be  scraped  from  the  shell 
and  tubes  at  this  point,  it  may  be  found  better  to  dis- 
charge at  the  side  near  the  rear  and  just  below  the  water 
line. 

If  for  any  reason  the  blow-off  pipe  cannot  be  arranged 
so  that  it  can  be  properly  protected  from  the  fire  (and 
occasionally. this  is  the  case),  and  if  a  good  heater  is 
used,  there  is  no  great  objection  to  feeding  through 
the  blow-off  if  that  is  the  preference  of  the  engineer. 
It  is  always  well  to  have  both  systems  installed  so  that 
if  one  fails  the  other  may  be  used. 


XIII 

CARE  AND  MANAGEMENT  OF  BOILERS1 

THERE  has  been  a  great  deal  written  by  different 
authors  on  the  subject  of  care  and  management  of 
boilers.  Valuable  advice  has  been  given,  yet  boiler 
explosions  and  accidents  still  occur.  Therefore,  too 
much  cannot  be  said  to  impress  upon  the  mind  of  the 
stationary  engineer  the  importance  of  taking  care  of 
boilers. 

The  first  and  most  important  thing  to  begin  with  is 
a  good,  sound  boiler,  for  if  the  boiler  is  an  old  and  dilapi- 
dated concern  the  best  and  most  skilful  engineer  can- 
not make  it  safe  and  reliable,  and  the  only  advice  in 
any  case  like  this  would  be  to  have  nothing  to  do  with 
it,  as  not  only  his  reputation  as  an  engineer  would  be 
at  stake  but  also  his  life  and  the  lives  of  others. 

When  taking  charge  of  a  plant  that  has  been  run  for 
some  time  the  engineer  should  lose  no  time  in  ascer- 
taining as  far  as  possible  the  exact  condition  of  the 
boilers,  and  at  the  first  opportunity  he  should  make  an 
internal  and  external  examination  and  see  that  they 
are  free  from  scale  and  incrustation.  If  they  are  not, 
he  should  see  that  they  are  thoroughly  cleaned  both 
inside  and  outside  of  the  shell.  When  a  boiler  is  once 

1  Contributed  to  Power  by  John  McConnaughy. 
145 


146  BOILERS 

thoroughly  cleaned  the  competent  engineer  will  always 
resort  to  the  proper  means  of  keeping  it  so  far  as  con- 
ditions will  allow. 

The  accumulation  of  scale  can  be  in  a  measure 
avoided  by  blowing  small  quantities  of  water  from  the 
bottom  and  surface  blow-off,  as  all  minerals  held  in 
suspension  become  of  greater  specific  gravity  than  the 
water.  When  heated,  the  tendency  by  specific  gravity 
is  to  settle  toward  the  bottom  while  the  lighter  portions 
remain  upon  the  top  and  float  in  the  form  of  a  scum. 
It  has  been  found  that  by  frequently  blowing  from  the 
surface  and  bottom  blow-off,  much  of  the  mineral 
substance  which  forms  scale  will  be  carried  out  before 
it  can  settle  sufficiently  to  attach  itself  to  the  iron. 
By  so  doing,  much  of  the  trouble  from  scale  may  be 
avoided. 

Notwithstanding  all  the  care  that  may  be  taken, 
in  some  localities  where  the  water  is  largely  impreg- 
nated with  minerals  a  certain  amount  of  scale  will 
accumulate  in  spite  of  the  efforts  of  the  most  careful 
and  experienced  engineer.  There  are  various  devices 
and  compounds  on  the  market  which  have  proved 
effective  and  in  a  measure  beneficial  for  preventing 
this  scale.  Others  are  of  a  doubtful  character;  it  is 
advisable  before  using  a  compound  to  have  a  chemical 
analysis  made  of  the  feed-water,  as  the  nature  of  the 
supply  receives  too  little  attention. 

Some  engineers  having  charge  of  boilers  with  man- 
holes under  the  tubes  do  all  their  cleaning  from 
below  the  tubes  and  do  not  open  the  boiler  on  top. 
As  it  is  impossible  to  wash  all  the  dirt  down  from  the 


CARE   AND   MANAGEMENT   OF   BOILERS         147 

top  by  washing  from  the  under  side  of  the  tubes,  the 
boiler  is  in  bad  condition  above  the  tubes  before  they 
know  it  and  they  will  tell  you  that  the  boilers  are  in 
good  shape  inside. 

In  cleaning  boilers,  all  manholes  and  hand-hole 
plates  should  be  taken  out  and  the  washing  should  be 
done  from  above  and  below  the  tubes.  The  engineer 
should  then  go  inside  the  boiler  and  clean  between  them, 
so  that  any  scale  that  has  been  lodged  between  the 
tubes  can  be  taken  out.  On  the  outside,  all  seam  heads 
and  tube  ends  should  be  examined  for  leaks,  cracks, 
corrosions,  pitting  and  grooving.  The  condition  of 
stays,  braces  and  their  fastenings  should  be  examined. 
The  shell  of  the  boiler  should  be  thoroughly  cleaned 
on  the  outside,  as  soot  is  a  bad  conductor  of  heat,  holds 
dampness  and  is  liable  to  cause  corrosion.  All  valves 
about  the  boiler  should  be  kept  clean  and  in  good 
working  condition.  The  pumps  or  injectors  should  be 
in  the  best  working  order.  The  connections  between 
the  boiler  and  water  column  and  also  the  gage  glass 
should  receive  the  closest  attention,  but  they  are  sadly 
neglected  by  some  engineers.  The  brickwork  should 
be  kept  in  good  condition  and  all  air  holes  stopped,  as 
they  decrease  the  efficiency  of  the  boiler  and  are  liable  to 
cause  injury  to  the  plates  by  burning. 

There  should  be  a  good  heater  in  connection  with  the 
boiler  and  the  feed-water  as  hot  as  you  can  work  it,  for 
feeding  cold  water  causes  too  much  contraction  and 
expansion.  This  causes  vibration  in  the  seams  and 
makes  them  weak  at  those  points.  For  example,  if 
one  hundred  pounds  of  steam  will  do  your  work;  never 


1 48  BOILERS 

carry  any  more  nor  less,  as  the  rise  and  fall  in  pressure 
causes  expansion  and  contraction  of  the  plates. 

Never  open  the  fire  doors  to  cool  your  boiler.  Close 
the  ash-pit  doors  and  open  the  smoke-box  doors  in 
case  you  get  too  much  steam,  as  opening  the  fire  door 
causes  too  much  contraction  by  the  cold  air  cooling 
the  furnace.  It  would  be  better  to  allow  steam  to 
blow  off  from  the  safety  valve,  which  will  not  in  any 
way  injure  the  boiler. 

The  safety  valve  should  be  raised  from  its  seat  every 
day  to  make  sure  it  does  not  stick  from  any  cause,  and 
observe  from  the  steam  gage  if  the  valve  blows  off  at 
the  pressure  it  is  set  for. 

It  is  of  the  highest  importance  to  keep  the  blow-off 
pipe  free  from  sediment  of  any  kind,  as  the  pipe  is  liable 
to  fill  up  and  burn  off,  and  the  only  way  to  keep  it  free 
is  to  open  the  blow  cock  often  enough  to  keep  every- 
thing flushed  out. 

The  best  time  to  blow  off  is  in  the  morning  before 
the  fires  have  been  started  up,  as  a  good  deal  of  sediment 
in  the  boiler  will  then  have  settled  to  the  bottom  of 
the  shell  and  much  of  it  will  pass  out  when  the  cock  is 
opened.  Noon  is  also  a  good  time,  after  the  fires  have 
been  banked  for  half  an  hour  or  more,  so  that  the  water 
in  the  boiler  has  been  quiet  long  enough  to  deposit 
the  particles  that  are  being  whirled  about  with  it 
through  all  parts  of  the  boiler. 

When  a  blow-off  cock  is  opened,  it  must  be  remem- 
bered that  it  is  not  to  be  yanked  wide  open  and  then 
closed  the  same  way.  This  practice  is  very  dangerous. 
No  valve  about  a  steam  system  ought  to  be  closed 


CARE   AND   MANAGEMENT  OF  BOILERS         149 

suddenly,  except  in  time  of  emergency,  because  the 
sudden  strain  on  the  pipe  and  fittings  is  liable  to  cause 
a  rupture  in  the  pipe  or  else  break  the  elbow  or  valve. 
The  boiler  is  the  life  of  any  plant  and  my  advice 
to  all  owners  of  steam  plants  is  to  keep  a  first-class 
engineer,  one  who  is  strictly  temperate,  pay  him  good 
wages,  give  him  the  necessary  material,  and  his  plant 
will  get  the  proper  care  and  management. 


XIV 

SETTING  RETURN  TUBULAR  BOILERS 

A  GREAT  improvement  is  made  when  we  discard  the 
old-time  setting  of  return-tubular  boilers,  in  which 
cast-iron  brackets  were  supported  by  brick  walls  which 
are  constantly  crumbling  away,  for  the  substantial 
form  of  setting  which  is  obtained  by  suspending  return- 
tubular  boilers  from  I-beams  supported  by  cast-iron 
columns. 

The  accompanying  Figures  77  and  78  show  the 
setting  of  boilers  in  single  or  double  batteries.  In  set- 
ting an  even  number  of  boilers,  as  six  or  eight  in  one 
setting,  it  is  best  to  divide  them  into  pairs  so  that 
not  more  than  two  boilers  will  be  suspended  between 
supports. 

The  principal  reason  for  this  is  that  when  the  large 
sizes,  such  as  from  150  to  250  horse-power- are  used, 
the  size  I-beam  required  to  safely  carry  this  load 
between  supports  is  so  large  that  it  overbalances  the 
cost  of  two  or  more  cast-iron  columns. 

In  setting  an  odd  number  of  boilers,  such  as  three  or 
five,  in  a  battery,  columns  are  usually  placed  between 
each  boiler  with  a  2-inch  air  space  all  around  the  column 
and  an  air  duct  at  the  bottom  of  the  setting  which  runs 
through  from  the  front  to  the  back  and  connects  with 


SETTING    RETURN   TUBULAR   BOILERS 


BOILERS 


SETTING    RETURN   TUBULAR   BOILERS          153 

each  air  space  around  the  column.  This  keeps  up 
a  circulation  of  air  and  the  columns  are  kept  com- 
paratively cool. 

In  setting  boilers  in  this  manner  the  columns  and 
I-beams  are  set  in  position  first.  Then  the  boiler  is 
hoisted  to  the  proper  hight  by  means  of  tackle  which  is 
fastened  to  the  I-beams  and  when  the  boiler  is  brought 
to  the  proper  hight  the  U-bolts  are  slipped  into  place 
and  fastened  by  nuts  and  washers  to  the  I-beams. 
This  does  away  with  the  use  of  blocking  and  barrels 
which  are  generally  used  and  leaves  all  the  space  clear 
under  the  boilers. 

The  expansion  is  easily  taken  care  of  by  the  U-bolts 
and  hangers,  as  is  shown  in  the  setting  plans,  and  if  the 
walls  are  properly  set,  they  should  show  no  cracks 
as  they  carry  no  weight  and  are  entirely  free. 

The  accompanying  table  has  been  carefully  worked 
out  with  a  factor  of  safety  of  5  and  gives  the  different 
lengths  and  sizes  of  I-beams  and  columns  required,  so 
that  a  person  estimating  on  a  job  of  this  kind  can 
readily  determine  the  cost  of  such  a  setting.  It  covers 
boilers  from  36  inches  in  diameter  and  8  feet  long  to  90 
inches  and  20  feet,  giving  the  total  weight  to  be  sup- 
ported and  the  sizes,  weights  and  positions  of  columns 
and  I-beams  required. 


154 


BOILERS 


SIZES  AND   WEIGHTS  OF   COLUMNS  AND   I-BEAMS   RE 


HORSE   POWER 

i5 

20 

25 

3° 

35 

40 

45 

50 

60 

Dia.  of  boiler  in  inches   

36 

36 

42 

42 

44 

48 

50 

54 

54 

Length  of  tubes  in  feet  

8 

10 

10 

12 

12 

12 

13 

13 

15 

Length    of    curtain    sheet    in 

inches  

ii 

II 

12 

12 

12 

14 

14 

14 

14 

Total    weight    of    boiler    and 

7500 

10500 

13300 

15300 

water  

6500 

9400 

II500 

14200 

17800 

Rear  head  to  center  of  hanger 
Center  to  center  of  hangers    . 

2-0 

4~0 

2-6 

5-0 

2-6 

S~0 

3-0 

6-0 

3-0 

6-0 

3-o 
6-0 

3-3 
6-6 

3-3 
6-6 

3-9 

7-6 

Front  head  to  center  of  hanger 

2-0 

2-6 

2-6 

3-o 

3-o 

3-o 

3-3 

3-3 

3-9 

Distance   between   C  of  sup- 

ports (i  boiler)   

6-6 

6-6 

7-0 

7-0 

7-2 

7-6 

7-8 

8-0 

8-0 

Distance   between   C  of  sup- 

ports (2  boilers)    

1  1-8 

1  1-8 

12-8 

12-8 

13-0 

13-8 

14-0 

14-0 

14-8 

Length  of  I-beam  for  i  boiler  . 
Length  of  I-beam  for  2  boilers  . 

7~3 
12-6 

7-3 
12-6 

7-10 
13-8 

7-10 

13-8 

S-o 
14-0 

8-4 
14-8 

8-6 

15-0 

8-10 
15-10 

8-10 
15-10 

Size   of   I-beam   required   for 

one  boiler  

4 

4 

5 

5 

5 

6 

6 

6 

6 

Size  of  I-beam  required  for  2 

boilers  

6 

6 

8 

8 

9 

9 

9 

10 

10 

Weight  per  ft.  of  I-beam   for 

one  boiler  

7-5 

7-5 

9-75 

9-75 

9-75 

12.25 

12.25 

12.25 

12.25 

Weight  per  ft.  of  I-beam    for 

two  boilers  

12.25 

12.25 

18 

18 

21 

21 

21 

25 

25 

Length  of  cast-iron  column   .  . 

8-0 

8-0 

8-6 

8-6 

8-8 

9-3 

9-5 

10-0 

10—  o 

Outside  Dia.  of  C.  I.  col.  for 

Outside  Dia.  of  C.  I.  col.  for 

5 

two  boilers  

5 

5 

5 

5 

5 

6 

6 

6 

6 

Size  of  flange  on  ends  of  col 

for  one  boiler  

94 

94 

10 

10 

10 

10* 

io4 

ro4 

104 

Size  of  flange  on  ends  of  col 

for  two  boilers  

104 

104 

12 

12 

124 

124 

12* 

13* 

134 

Thickness  of  C.  I.  col.  for  one 

boiler  

4 

i 

i 

i 

\ 

k 

4 

i 

\ 

Thickness  of  C.  I.  col.  for  two 

boilers  

1 

f 

i 

I 

\ 

\ 

f 

1 

\ 

SETTING    RETURN   TUBULAR   BOILERS 


155 


QUIRED   IN   SETTING   RETURN   TUBULAR   BOILERS. 


70 

75 

80 

90 

100 

125 

ISO 

175 

200 

200 

225 

225 

250 

60 

60 

60 

66 

66 

72 

72 

78 

78 

84 

84 

90 

90 

14 

15 

16 

i5 

16 

16 

18 

18 

2O 

18 

20 

18 

20 

16 

16 

16 

i7 

i? 

18 

18 

18 

18 

20 

20 

22 

22 

20800 

27200 

35000 

44000 

56000 

67000 

75000 

24800 

30300 

40000 

48000 

55ooo 

65000 

3-6 

3-9 

4-0 

3-9 

4-0 

4-0 

4-6 

4-6 

S-o 

4-6 

5-o 

4-6 

5-o 

7—0 

7-6 

8-0 

7-6 

8-0 

8-0 

9-0 

9-0 

i  o-o 

9-0 

i  o-o 

9-0 

i  o-o 

3-6 

3-9 

4-0 

3-9 

4-0 

4-0 

4-6 

4-6 

5-o 

4-6 

5-o 

4-6 

5-o 

9-0 

9-0 

9-0 

9-6 

9-6 

10—  o 

10—  o 

10-6 

10-6 

n-o 

II—  O 

1  1-6 

1  1-6 

1  6-2 

1  6-2 

1  6-2 

17-2 

17-2 

1  8-2 

1  8-2 

19-2 

19-2 

20-2 

20-2 

21-2 

21—2 

1  0-0 

10—  o 

10-0 

10-6 

10-6 

1  1—  O 

1  I—  O 

11-7 

11-7 

12—  O 

I2-O 

12-6 

12-8 

17-4 

17-4 

17-4 

1  8-4 

18-4 

19-5 

19-5 

20-6 

20-6 

21-6 

21-6 

22-6 

22-6 

7 

7 

7 

7 

7 

8 

8 

9 

9 

9 

9 

9 

10 

12 

12 

12 

12 

12 

IS 

15 

IS 

IS 

15 

15 

IS 

15 

IS 

31-5 

!5 
31-5 

J5 
3i-5 

15 

40 

40 

42 

42 

60 

60 

60 

80 

80 

25 

80 

10-8 

10-8 

10-8 

1  1-2 

I  1-2 

12-0 

12—  O 

12—6 

12-6 

13-0 

13-0 

13-10 

13-10 

5 

5 

5 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

6 

8 

8 

8 

8 

8 

8 

8 

8 

»i 

ii* 

ii* 

II* 

ii* 

12 

12 

12* 

12* 

12* 

12* 

12* 

13* 

i4 

14 

14 

14* 

14* 

IS 

15 

16 

1  6 

1  6 

I? 

17 

i7 

} 

i 

! 

f 

3 

3 

3 

i 

i 

i 

I 

I 

i 

i 

! 

f 

1 

I 

3 

f 

! 

i 

i 

1 

I 

XV 


RENEWING  TUBES    IN   A   TUBULAR 
BOILER1 

WHILE  the  renewal  of  boiler  tubes  is  properly  the 
work  of  the  boiler  maker,  the  engineer  who  knows 
how  to  and  can  do  it  is  just  so  much  more  valuable 
to  the  employer.  The  purpose  of  this  article  is  to  de- 
scribe the  method  employed,  together  with  the  tools 
required. 

First,  it  is  essential  to  place  a  distinguishing  mark 
on  the  front  and  rear  heads  to  show  which  tube  is  to 
be  cut  out,  using  chalk  or  soapstone  for  the  purpose, 
and  the  best  way  to  make  sure  that  the  helper  at  the 
other  end  of  the  boiler  marks  the  same  tube  that  you 
do  is  to  run  through  a  strip  of  wood  four  or  five  inches 
longer  than  the  tube.  As  such  a  strip  is  of  use  farther 
along  in  the  process  it  is  well  to  make  a  length  of  J  X  2- 
inch  pine  to  serve  both  purposes.  Next,  with  a  hammer 
and  a  heavy  cape  chisel  having  a  wide  cutting  edge, 
which  is  less  liable  to  cut  or  mar  the  boiler  (see  Fig.  79), 
face  the  beads  on  both  ends  of  the  old  tube  until  they 
are  flush  with  the  heads  of  the  boiler.  Then,  at  the 
front  head,  with  a  diamond-point  chisel  such  as  is  shown 
in  Fig.  80,  cut  a  slot  or  channel,  TV  inch  wide,  in  the 

1  Contributed   to  Power  by   J.   E.   Sexton. 
156 


RENEWING   TUBES   IN   A  TUBULAR   BOILER    157 

bottom  of  the  tube,  extending  inward  to  about  f  of  an 
inch  beyond  the  inner  edge  of  the  head,  making  sure 
that  the  groove  is  cut  in  the  tube  only  and  that  the  head 


FIG.  79. 

is  not  cut  or  even  marked  by  the  chisel.    Do  not  drive 
the  chisel  clear  through  the  tube,  either. 
With  an  offset  chisel,  Fig.  81,  carefully  turn  up  the 


FIG.  80. 


edges  of  the  tube  at  both  sides  of  the  cut,  until  the 
tube-end  resembles  the  condition  shown  in  Fig.  82, 
when  it  will  be  found  that  this  end  of  the  tube  has 


FIG.  81. 


been  released  from  the  head.  In  cutting  the  slot, 
especially  after  the  cutting  edge  of  the  chisel  has  gone 
beyond  the  thickness  of  the  head,  if  the  chisel  is 
allowed  to  go  through  the  tube  it  will  be  the  source  of 


158 


BOILERS 


considerable  trouble,  as  it  will  cause  the  tube  to  spread. 
Hence,  at  this  point  extreme  care  must  be  used. 

If  a  tube  is  corroded  and  muddy,  it  will  be  harder  to 
remove  and  the  method  will  have  to  be  changed  some- 
what. Considerable  force  is  required  sometimes  to 
remove  such  a  tube.  Instead  of  one  slot  in  the  bottom 
of  the  tube,  two  are  cut,  about  f  of  an  inch  apart,  and 


FIG.  82. 

the  offset  chisel  is  used  as  before,  except  that  the  f- 
inch  piece  is  turned  up  until  it  looks  like  the  letter  C, 
with  its  back  toward  the  front  of  the  boiler.  Then  pro- 
ceed as  before,  turning  the  edges  of  the  cut  upward 
as  far  as  they  will  go.  A  hook  on  the  end  of  a  chain 
or  rope  may  then  be  inserted  in  the  loop  formed  by 
the  C-piece.  This  takes  care  of  the  front  end. 

At  the  other  end  of  the  tube  insert  the  end  of  a  piece 
of  shafting  about  10  inches  long  and  a  little  smaller 
in  diameter  than  the  outside  diameter  of  the  tube. 


RENEWING   TUBES   IN   A   TUBULAR   BOILER        159 

The  end  of  this  shafting  should  be  turned  so  that  it  will 
enter  the  tube  about  one  inch,  with  an  easy  fit,  and  by 
giving  a  few  taps  on  the  outer  end  of  this  improvised 
mandrel  the  tube  will  be  loosened  at  this  end.  Then, 
by  working  the  tube  backward  and  forward  it  can  be 
released  altogether. 

The  next  step  is  to  mark  the  new  tube  so  it  can  be  cut 
to  length.  Insert  the  Jx2-inch  piece  of  pine  into  the 
holes  the  old  tube  came  out  of  until  one  end  of  the  strip 
extends  through  the  rear  head  about  ^  of  an  inch. 
Hold  it  there  and  proceed  to  place  a  mark  on  the  end 
extending  from  the  front  head  &  of  an  inch  from  face 
of  the  head.  This  gives  the  proper  length  to  which 
to  cut  the  new  tube.  Then,  while  the  tube  is  being  cut 
to  length,  take  a  half-round  second-cut  file,  or  a  finish- 
cut  file,  and  carefully  smooth  up  the  heads  around  the 
holes,  removing  any  marks  or  cuts  which  may  have 
been  made  in  taking  out  the  old  tube.  This  is  to  pre- 
vent future  leaks.  Next,  push  the  new  tubes  into  place 
and  station  the  helper  at  the  rear  end  with  a  tube 
expander,  being  sure  that  the  ends  of  the  tube  are  equi- 
distant from  the  heads.  It  is  advisable  to  insert  one 
end  of  an  8-foot  section  of  i-inch  pipe  in  the  front  end 
of  the  tube,  for  a  distance  of  12  inches  or  so,  and  exert 
a  downward  pressure  on  the  lever  so  provided  to  pre- 
vent the  tube  from  turning  while  the  rear  end  is  being 
expanded.  As  soon  as  the  tube  is  tight  at  the  rear  end, 
proceed  to  expand  the  front  end. 

A  self-feeding  expander,  Fig.  83,  will  give  good 
results,  especially  if  a  ratchet  wrench  is  used  to  turn 
the  spindle,  for  one  can  tell  by  the  feeling  just  when 


i6o 


BOILERS 


to  stop  expanding.    A  monkey  wrench  will  do,  however, 
if  a  ratchet  wrench  is  not  available. 

The  beading  comes  next.  This  requires  a  special 
tool  similar  to  that  shown  in  Fig.  84.  Place  the  long 
prong  of  the  tool  inside  the  tube,  with  the  short  prong 
pressing  against  the  tube-end.  Then  bead  the  tube-end 


FIG.  83. 

thoroughly  throughout  the  circumference,  for  if  it  is 
only  beaded  here  and  there  it  will  prove  very  unsatis- 
factory. When  both  ends  are  beaded,  use  the  expander 
lightly  in  each  end  once  more,  to  remove  the  marks 
made  by  the  beader. 


If  both  hand-hole  plates  are  tight  and  the  blow-off 
valve  works  O.  K.,  fill  the  boiler  with  either  hot  or  cold 
water,  until  the  tube  is  covered,  and  if  the  tube  does 
not  leak  water  it  will  hold  steam,  and  the  boiler  is  ready 
to  put  into  commission.  If  the  tube  leaks,  re-expand 
it  very  lightly.  Ordinarily,  a  man  and  helper  can 
renew  a  tube  in  an  hour,  with  ease. 


XVI 

USE   OF   WOOD   AS    FUEL   FOR   STEAM 
BOILERS1 

IN  nearly  all  plants  where  lumber  or  wooden  articles 
are  the  finished  products,  wood  is  used  as  a  fuel  for  the 
boilers,  because  it  is  a  refuse  and  is  easily  and  cheaply 
disposed  of  in  that  manner.  In  some  plants  the  amount 
of  this  refuse  is  greater  than  can  be  burned  under  the 
boilers;  in  others,  there  is  not  enough  waste  to  furnish 
the  steam  required. 

This  is  the  case  in  a  great  many  wood-working 
industries,  and  in  some  sawmills  on  the  South  Atlan- 
tic coast.  To  this  class  of  industries  this  article  is  di- 
rected. 

A  certain  wood  is  a  good  fuel  or  a  poor  fuel,  depending 
on  (i)  the  moisture  contained  and  (2)  the  size  of  the 
pieces  as  fired.  Whether  it  burns  well  under  the  boiler 
depends  on  the  shape  of  the  furnace,  the  method  of 
firing  and  the  draft  of  the  chimney. 

CALORIFIC  VALUE  OF  VARIOUS  WOODS 

The  main  idea  to  be  shown  in  this  section  is  that  the 
value  of  all  woods  is  about  the  same,  depending  on  the 
amount  of  moisture  contained. 

1  Contributed  to  Power  by  J.  A.  Johnston. 
161 


162  BOILERS 

In  various  works  of  reference,  the  weight  of  one  cord 
of  different  woods  (thoroughly  air-dried)  is  about  as 
follows,  the  quality  of  coal  not  being  given  : 

Hickory  or  hard  maple  —  4500  Ib.  equals  1800  Ib. 
of  coal  (others,  2000  Ib.). 

White  oak  —  3850  Ib.  equals  1  540  Ib.  of  coal  (others, 
1715  Ib.). 

Beech,  red  and  black  oak  —  3250  Ib.  equals  1300  Ib. 
of  coal  (others,  1450  Ib.). 

Poplar,  chestnut  and  elm  —  2350  Ib.  equals  940  Ib. 
of  coal  (others,  1050  Ib.). 

Average  pine  —  2000  Ib.  equals  800  Ib.  of  coal 
(others,  925  Ib.). 

Referring  to  the  figures  last  given  in  each  case  in 
connection  with  "others,"  it  is  said: 

"  From  the  above  it  is  safe  to  assume  that  2\  pounds 
of  dry  wood  are  equal  to  i  pound  of  average  quality  soft 
coal,  and  that  the  fuel  value  of  different  woods  is  very 
nearly  the  same,  that  is,  a  pound  of  hickory  is  about 
equal  to  a  pound  of  pine,  assuming  both  to  be  dry." 

It  is  important  that  the  woods  be  dry  in  the  com- 
parison, as  each  10  per  cent,  of  water  or  moisture 
in  the  wood  will  detract  about  12  per  cent.-  from  its 
fuel  value. 

Take  an  average  wood  of  the  chemical  analysis: 
Carbon,  51  per  cent.;  hydrogen,  6.5  per  cent.;  oxygen, 
42  per  cent.;  ash,  0.5  per  cent.  If  perfectly  dry,  its 
fuel  value  per  pound,  according  to  Dulong's  formula, 


V  =      i4,50oC  +  62,000 


=  Ti4,50oC 


USE   OF   WOOD   AS    FUEL   FOR   STEAM   BOILERS       163 

is  8170  B.t.u.  The  calorific  value  of  carbon  equals 
14,500  B.t.u.,  and  the  calorific  value  of  hydrogen 
equals  62,000  B.t.u. 

The  hydrogen  in  the  fuel  being  partly  in  combination 
with  the  oxygen,  only  that  part  not  in  such  combina- 
tion can  be  counted  on  as  a  fuel,  hence  the  factor 


(*-§) 


If  this  wood  as  ordinarily  dried  in  air  contains  25 
per  cent,  moisture,  then  the  heating  value  of  a  pound 
of  such  wood  is  8170  X  0.75  =  6127  B.t.u.,  less  the 
heat  required  to  raise  the  J  pound  of  water  from  atmos- 
pheric temperature  to  steam,  and  to  heat  this  steam  to 
chimney  temperature.  Say,  for  instance,  it  takes  150 
B.t.u.  to  heat  the  water  to  212  degrees  and  966  B.t.u. 
to  evaporate  it  to  steam,  and  100  B.t.u.  to  raise  the 
temperature  of  the  steam  to  chimney  temperature; 
in  all  1216  B.t.u.  per  pound  or  304  B.t.u.  per  J  pound. 
The  net  value  of  the  wood  as  a  fuel  would  then  be  6127 
-  304  =5824  B.t.u.,  or  about  0.4  that  of  i  pound  of 
carbon.  This  method  can  be  applied  to  any  wood, 
knowing  its  chemical  analysis  and  its  percentage  of 
moisture  as  burned. 

THE  MOISTURE  CONTENT 

As  nearly  all  woods  have  about  the  same  chemical 
analysis,  the  heat  value  of  woods  depends,  as  before 
mentioned,  almost  entirely  on  the  moisture  contained 
in  the  wood  when  burned.  When  newly  felled  wood 
contains  a  proportion  of  moisture  which  varies  much 


164  BOILERS 

in  different  kinds  and  different  specimens,  ranging 
between  30  and  50  per  cent.,  and  averaging  about  40 
per  cent.  Perfectly  dry  wood  contains  about  50  per 
cent,  of  carbon,  the  remainder  consisting  almost  entirely 
of  hydrogen  and  oxygen  in  the  proportion  which  forms 
water.  The  coniferous  (pines)  family  contains  a  small 
quantity  of  turpentine,  which  is  a  hydrocarbon.  The 
proportion  of  ash  in  wood  is  from  i  to  5  per  cent.  The 
total  heat  of  combustion  in  all  woods  is  almost  exactly 
the  same,  and  is  that  due  to  the  5O-per  cent,  carbon. 

American  woods  vary  in  percentage  of  ash  from  0.3 
to  1.2  per  cent.,  and  the  heat  value  ranges  from  6600 
B.t.u.  for  white  oak  to  9883  for  long-leaf  pine,  the  fuel 
value  of  0.5  pound  of  carbon  being  7272  B.t.u. 

In  the  absence  of  any  method  of  determining  the 
heating  value  of  a  certain  wood,  the  following  are 
averages  of  the  analyses  of  beech,  oak,  birch,  poplar, 
and  willow: 

Carbon,  per  cent  49-7° 

Hydrogen,  per  cent 6.06 

Oxygen,  per  cent 41 .30 

Nitrogen,  per  cent 1.05 

Ash,  per  cent i  .80 

These  can  be  used  in  the  foregoing  formula,  and  will 
give  an  approximate  value  for  nearly  all  American 
woods. 

A  very  good  and  fairly  accurate  approximation  of 
the  amount  of  moisture  in  any  particular  sample  can 
be  obtained  by  weighing  the  wood  (say  about  10  pounds 
of  it),  and  then  placing  the  sample  in  a  closed  vessel 


USE   OF   WOOD   AS    FUEL   FOR   STEAM    BOILERS       165 

with  a  small  hole  in  it  to  allow  the  steam  to  escape. 
Subjecting  the  whole  to  a  temperature  of  about  220 
degrees  until  all  the  moisture  has  been  driven  off, 
weigh  the  sample  again,  and  the  percentage  of  moisture 
in  the  original  can  be  computed  easily.  With  this  per- 
centage known,  the  subtraction  for  moisture  present 
can  be  made,  as  before  shown,  and  an  approximate 
value  of  the  sample  is  obtained. 

Nearly  all  woods  will  give  a  heat  value,  dry,  of  about 
8200  B.t.u.  Having  obtained  the  percentage  of 
moisture  present,  the  heat  value  of  the  fuel  is  8200 
multiplied  by  (100  per  cent.  —  per  cent,  moisture)  less 
(heat  required  to  raise  water  contained  to  evaporative 
point)  less  (heat  required  to  evaporate  water)  less 
(heat  required  to  heat  steam  made  by  this  water  to 
chimney-gas  temperature).  All  of  the  latter  quantities 
can  be  obtained  from  steam  tables. 

EASIEST  METHOD  FOR  GETTING  AT  THE  HEAT 
VALUE 

Probably  the  easiest  and  most  accurate  of  all  methods 
of  obtaining  the  heat  value  of  a  certain  specimen  of 
wood  is  not  to  inquire  into  the  chemical  analysis,  but 
to  take  a  sample  of  the  wood  just  in  the  condition  in 
which  it  is  burned,  place  it  in  a  closed,  air-tight  vessel, 
and  keep  it  there  until  it  is  brought  to  a  calorimeter. 
This  instrument  should  be  used  by  one  who  is  familiar 
with  its  use.  It  will  give  the  heat  value  expressed  as 
B.t.u.  per  pound,  dry.  The  percentage  of  moisture 
being  found,  the  correction  for  moisture  is  made  as 
before. 


i66  BOILERS 

A  case  of  this  kind,  taken  from  a  report  by  the  writer, 
may  be  mentioned  and  calculated.  The  fuel  was  sweet 
gum  refuse  from  a  veneer  mill,  run  through  a  hog  and 
ground  into  chips  approximately  the  size  of  a  man's 
little  finger.  The  logs  were  brought  to  the  mill  by 
rafting  down  a  river,  so  the  chips  as  fed  to  the  boilers 
were  not  out  of  the  water  over  three-quarters  of  an 
hour.  A  sample  of  chips  was  weighed  wet,  then  dried 
in  a  closed  vessel  and  weighed  again,  giving  a  moisture 
percentage  of  47.50.  A  sample  of  the  dried  wood  was 
then  ground  and  tested  in  a  calorimeter,  giving  a  heat 
value  of  8208  B.t.u.  per  pound,  dry. 

For  every  pound  of  the  wood  fired  there  was  only 
8208  X  0.525  =  4309  B.t.u.  given  up  by  the  wood  in 
burning,  for  there  was  but  i.oo  —  0.475  =  0.525 
pounds  of  dry  wood  fired  for  i  pound  of  fuel. 

One  pound  of  water  requires  966  B.t.u.  to  evaporate 
it  at  the  pressure  in  the  furnace.  There  was  0.475 
pound  of  water  in  the  i  pound  of  fuel  fired,  so  that 
966  X  0.475  =  4&l  B.t.u.  were  required. 

The  flue-gas  temperature  was  340  degrees  and  340  - 
212  =  128   B.t.u.   required  to  bring  the  steam  from 
the  boiling  point  to  the  chimney  temperatures.    The 
available  heat  in  the  wood  was,  then,  4309  —  461  - 
128  =  3702  B.t.u. 

Probably  the  greatest  chance  of  error  in  estimating 
the  value  of  a  wood  as  fired  is  to  neglect  the  above 
calculation,  because  the  difference  between  its  heating 
value  dry  and  its  heating  value  as  fired  is  often  as  high 
as  50  per  cent.,  while  a  similar  calculation  for  coal 
would  give  a  comparatively  small  difference. 


USE   OF   WOOD   AS   FUEL   FOR   STEAM   BOILERS       167 

After  computing  by  either  of  the  methods  given  the 
heat  value  of  the  fuel  to  be  burned,  it  is  easily  com- 
puted how  much  water  can  be  evaporated  per  pound 
of  fuel,  and  knowing  the  amount  of  available  fuel, 
the  power  to  be  generated  at  any  plant  under  considera- 
tion may  be  estimated. 

Referring  again  to  the  same  case  of  wet  gum  chips, 
this  fuel  was  brought  to  the  boiler  house  by  a  conveyer, 
the  average  capacity  being  measured  at  100  pounds 
per  minute,  or  6000  pounds  per  hour  brought  to  the 
boilers. 

A  pound  of  water  requiring  966  B.t.u.  to  evaporate 
it,  and  each  pound  of  the  fuel  having  3702  B.t.u., 
3702  +  966  =  3.83  pounds  of  water  per  i  pound  of 
fuel,  with  6000  pounds  of  fuel  per  hour,  the  maximum 
quantity  of  water  that  could  be  evaporated  by  the 
boilers  at  100  per  cent,  efficiency  would  be  6000  X  3.83 
=  22,980  pounds  per  hour. 

If  the  boiler  were  70  per  cent,  efficient,  22,980  X 
0.70  =  16,100  pounds  of  water  per  hour  evaporated 
from  and  at  212  degrees  is  all  that  could  be  expected, 
and  as  34^  pounds  of  water  per  hour  evaporated  from 
and  at  212  degrees  is  the  equivalent  of  one  boiler  horse- 
power, the  evaporation  given  would  represent  16,100 
+  34^  =  465  boiler  horse-power.  Under  test  the 
boilers  gave  450  boiler  horse-power. 

From  all  that  goes  before,  it  appears  that  wood  as  a 
fuel  has  been  allowed  a  little  too  high  a  value,  inasmuch 
as  it  is  rarely  if  ever  fed  to  the  boilers  perfectly  dry. 
It  is  generally  green,  and  in  cases  of  sawmills  located 
on  the  banks  of  navigable  streams  is  soaked  with  water. 


1 68 


BOILERS 


USE  OF  WOOD   AS   FUEL  FOR  STEAM   BOILERS      169 

Air-drying  of  wood  extracts  about  one-half  of  the 
moisture  in  a  year.  Wood  perfectly  dried,  and  then 
exposed  to  the  air,  will  absorb  about  the  same  amount 
of  moisture  that  it  would  contain  after  being  thoroughly 
air-dried.  However,  when  wood  is  to  be  used  as  a  fuel, 
it  is  almost  out  of  the  question  to  contemplate  drying 
it,  so  the  proposition  is  to  burn  the  fuel  available  in 

the  best  manner. 

FUEL  AVAILABLE 

Of  course  there  cannot  be  given  any  even  approxi- 
mate method  of  calculating  the  amount  of  fuel  that 
will  be  available  in  the  refuse  from  any  contemplated 
plant,  for  each  and  every  one  is  to  work  under  different 
conditions. 

In  plants  already  built,  an  estimate  can  be  made 
by  weighing  the  fuel  brought  to  the  boiler  room,  and 
by  foregoing  methods  determining  heat  value,  the 
available  horse-power  can  be  computed. 

Most  sawmills  furnish  enough  refuse  in  slabs  to  run 
the  boilers  required  to  operate  the  plant.  Wood- 
working plants,  sash,  blind  and  door  manufactories, 
furniture  factories,  etc.,  depend  entirely  on  the  kind 
of  product,  as  to  the  amount  of  scrap. 

This  will  also  depend  largely  on  the  plant  at  which 
the  installation  is  contemplated.  Furniture  factories, 
woodworking  plants,  etc.,  generally  work  the  kiln- 
dried  lumber  up  so  closely  that  the  refuse  as  it  comes 
to  the  boiler  is  already  in  an  easily  burnable  condition, 
that  of  sawdust,  shavings,  or  small  strips  or  blocks. 
These  can  be  fed  directly  to  the  furnace  without  further 
preparation. 


I  yo  BOILERS 

In  most  sawmills  where  the  slabs  come  off  of  the  logs 
in  long  pieces,  it  is  not  possible  to  get  the  fuel  to  burfi 
easily  if  fed  as  slabs,  so  it  is  often  and  generally  in  the 
sawmills  on  the  Atlantic  coast  fed  through  a  hog  which 
grinds  the  slabs  into  chips  varying  in  size  from  a  man's 
three  fingers  to  one  finger  or  smaller. 

This  is  undoubtedly  the  best  way  in  which  to  intro- 
duce this  fuel  to  the  boiler,  for  it  is  then  easily  handled 
by  conveyers,  and  can  be  dumped  directly  into  the  fire 
without  any  manual  work,  while  slabs  will  generally 
require  handling,  unless  some  extra  design  is  prepared 
to  meet  the  case.1 

The  various  forms  in  which  wood  is  fed  to  the  furnace 
may  be  summarized  as:  Cordwood,  shavings,  sawdust, 
dust  from  a  hog,  strips  and  blocks  from  a  factory,  and 

tan-bark. 

KIND  OF  FURNACE  REQUIRED 

Efficient  burning  of  wood  requires  a  large  combustion 
chamber,  and  grates  arranged  to  prevent  admission 
of  a  surplus  of  air.  This  cannot  be  obtained  to  good 
advantage  in  the  usual  coal-burning  furnace,  so  the 
dutch  oven  has  been  developed  to  meet  requirements. 
This  is  an  extension  of  the  fire-box  in  front  of  the  boiler, 
as  shown  in  Fig.  86,  with  a  firing  hole  in  the  top 
through  which  the  ground  fuel  or  sawdust  can  be  fed 
directly  from  the  conveyer  or  chute  to  the  grate. 

As  wood  fuel  is  generally  wet,  or  contains  a  large 
amount  of  moisture,  the  conditions  of  success,  as 
pointed  out  by  Thurston,  are:  To  surround  the  mass 
so  completely  with  heated  surfaces  and  with  burning 

1  A  case  of  this  kind  is  mentioned  in  Power,  November,  1907. 


USE   OF  WOOD  AS   FUEL   FOR  STEAM   BOILERS       171 


1 72  BOILERS 

fuel  that  it  may  be  rapidly  dried,  and  so  arranging  the 
apparatus  that  thorough  combustion  may  be  then 
secured,  the  rapidity  of  combustion  being  precisely 
equal  to,  and  never  exceeding,  the  rapidity  of  drying. 
If  the  proper  rate  of  combustion  is  exceeded,  the  dry 
portion  is  consumed  completely,  leaving  an  uncovered 
mass  of  fuel  which  refuses  to  take  fire. 

These  conditions  are  met  in  the  dutch  oven,  because 
of  the  fact  that  the  fire  is  completely  surrounded  by 
fire-brick  walls,  which  become  heated  to  a  very  high 
temperature,  especially  in  the  case  of  burning  pine 
shavings.  This  condition  of  good  burning  has  been  so 
well  met  in  some  cases  that  the  fire-brick  lining  could 
not  withstand  the  high  temperature  longer  than  a 
month. 

The  dutch  oven  has  a  firing  door  and  an  ash  door 
on  the  front;  the  firing  door  may  be  used  to  fire  any 
large  pieces  of  wood,  but  results  are  best  where  the  fire 
door  on  the  front  is  never  opened  except  for  cleaning. 

Fig.  87  shows  an  arrangement  where  the  fuel  con- 
sisted almost  entirely  of  kiln-dried  refuse  from  a  wood- 
working plant,  coming  to  the  boilers  in  short  sticks 
from  about  ^  X  J  X  12  inches  to  blocks  i  X  3  X  10 
inches,  all  mixed  with  sawdust  and  shavings  from 
planers. 

In  the  boiler  room  the  floor  is  on  an  exact  level 
with  the  top  of  the  dutch  oven.  The  fuel  is  dumped 
from  a  conveyer  on  this  floor  and  shoved  by  hand  into 
the  holes  on  top  of  the  ovens,  and  as  the  holes  are  kept 
full  of  fuel  all  the  time,  the  doors  over  them  are  never 
closed.  The  boilers  are  of  the  Heine  water-tube  type, 


USE  OF  WOOD  AS  FUEL  FOR  STEAM   BOILERS      173 


174  BOILERS 

arranged  in  a  battery  of  three  and  each  rated  at  300 
horse-power.  This  installation  gives  perfect  satisfac- 
tion. 

Another  form  of  combustion  chamber,  shown  in  Fig. 
85,  is  very  satisfactory  for  burning  sawdust  with  a  small 
mixture  of  shavings.  The  grate  must  be  kept  covered 
all  the  time,  or  too  much  air  Will  get  through,  thereby 
decreasing  the  efficiency  of  the  boiler.  In  this  case  the 
fuel  is  fed  in  a  constant  stream  from  a  chute  and  is 
shoved  back  over  the  grate  by  a  man  on  the  firing  floor. 

For  ordinary  air-dried  cordwood,  a  good  grate  is  one 
placed  at  the  firing-floor  level,  the  area  of  grate  being 
reduced  to  about  two-fifths  the  amount  required  for 
coal  by  sloping  the  furnace  walls  inward,  beginning 
just  under  the  arch.  The  grate  is,  of  course,  at  the 
bottom,  and  the  cordwood  can  be  carried  to  a  depth 
of  30  to  36  inches,  so  that  the  freshly  fired  wood  will 
crowd  down  that  which  is  partly  burned,  filling  the 
large  interstices  at  the  bottom  with  burning  coals, 
and  preventing  leakage  of  air  past  the  fire. 

MISCELLANEOUS  POINTS 

In  handling  any  kind  of  wood  fuel,  it  is  better,  even 
in  small  installations,  to  have  the  fuel  brought  by  some 
carrier,  as  a  conveyer,  chute  or  air  blast,  to  the  furnace. 
With  dry  wood  in  small  pieces,  as  dust  from  a  hog,  or 
shavings,  the  fuel  being  brought  to  the  fire-room,  one 
man  can  care  for  about  300  horse-power  of  boilers. 
If  it  is  brought  right  over  the  firing  hole  to  a  dutch 
oven  by  an  overhead  carrier,  he  can  care  for,  in  some 
cases,  500  horse-power. 


USE    OF   WOOD    AS    FUEL    FOR   STEAM    BOILERS      175 

Sawdust  and  dry  shavings  are  very  extensively 
handled  by  blowers,  the  suction  of  the  blower  being 
connected  to  the  saw  frame  or  planer,  and  the  refuse 
being  blown  into  a  receptacle  over  the  boiler  room. 
It  is  then  dropped  by  chutes  directly  into  the  fire,  or 
may  be  blown  directly  in  by  the  blast  furnishing  air  for 
the  fire. 

A  chimney  could  be  designed  from  theoretical  calcu- 
lations involving  the  chemical  composition  of  the  wood 
to  be  burned,  but  as  a  plant  burning  wood  is  rarely  or 
practically  never  run  on  a  Weight  basis,  this  would  not 
be  a  practical  method. 

It  has  been  borne  out  by  practice  that  a  chimney 
designed  for  a  certain  horse-power  for  bituminous  coal 
will  work  well  for  wood.  The  accompanying  curves 
were  calculated  from  Kent's  formula: 


In  Figs.  88  and  89,  with  any  boiler  horse-power  and 
any  suitable  hight,  the  area  of  stack  can  be  found.  In 
Fig.  90  this  area  is  expressed  for  round  or  square  stacks. 


176 


BOILERS 


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USE    OF    WOOD    AS   FUEL    FOR    STEAM    BOILERS      177 


1 78 


BOILERS 


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XVII 

BOILER    RULES 

THE  Board  of  Boiler  Rules  appointed  under  a  recent 
act  of  the  Massachusetts  legislature  has  adopted  the 
following  regulations: 

SECTION  i  —  MAXIMUM  PRESSURE  ON  BOILERS 

1.  The  maximum  pressure  allowed  on  any  steam 
boiler  constructed  wholly  of  cast   iron  shall  not   be 
greater  than  twenty-five   (25)  pounds  to  the  square 
inch. 

2.  The  maximum  pressure  allowed  on  any  steam 
boiler  the  tubes  of  which  are  secured  to  cast-iron  headers 
shall  not  be  greater  than  one  hundred  and  sixty  (160) 
pounds  per  square  inch. 

3.  The  maximum  pressure  allowed  on  any  steam 
boiler  constructed  of  iron  or  steel  shells  or  drums  shall 
be  calculated  from  the  inside  diameter  of  the  outside 
course,  the  percentage  of  strength  of  the  longitudinal 
joint  and  the  minimum  thickness  of  the  shell  plates; 
the  tensile  strength  of  shell  plates  to  be  taken  as  fifty- 
five  thousand  pounds  per  square  inch  for  steel  and  forty- 
five  thousand  pounds  per  square  inch  for  iron,  when 
the  tensile  strength  is  not  known. 


179 


i8o  BOILERS 

SHEARING  STRENGTH  OF  RIVETS 

4.  The  maximum  shearing  strength  of  rivets  per 
square   inch  of  cross-sectional  area   to  be   taken   as 
follows : 

Iron  rivets  in  single  shear   38,000  Ib. 

Iron  rivets  in  double  shear    70,000  Ib. 

Steel  rivets  in  single  shear 42,000  Ib. 

Steel  rivets  in  double  shear 78,000  Ib. 

FACTORS  OF  SAFETY 

5.  The  lowest  factors  of  safety  used  for  steam  boilers 
the  shells  or  drums  of  which  are  directly  exposed  to  the 
products  of  combustion,  and  the  longitudinal  joints  of 
which   are   of   lap-riveted   construction,    shall    be   as 
follows : 

(a)  Five  (5)  boilers  not  over  ten  years  old. 

(b)  Five  and  five-tenths  (5.5)  for  boilers  over  ten 
and  not  over  fifteen  years  old. 

(c)  Five    and    seventy-five    hundredths    (5.75)    for 
boilers  over  fifteen  and  not  over  twenty  years  old. 

(d)  Six  (6)  for  boilers  over  twenty  years' old. 

(e)  Five  (5)  on  steam  boilers  the  longitudinal  joints 
of  which  are  of  lap-riveted  construction,  and  the  shells 
or   drums  of  which  are  not  directly  exposed  to  the 
products  of  combustion. 

(/)  Four  and  five-tenths  (4.5)  on  steam  boilers  the 
longitudinal  joints  of  which  are  of  butt  and  strap 
construction. 


BOILER  RULES  181 

SECTION  2 

Section  2  sets  forth  the  standard  form  of  certificate 
of  annual  inspection. 

SECTION  3  —  FUSIBLE  PLUGS 

1.  Fusible  plugs,  as  required  by  section  20,  chapter 
465,  Acts  of  1907,  shall  be  filled  with  pure  tin. 

2.  The  least  diameter  of  fusible  metal  shall  not  be 
less  than  one-half  (J)  inch,  except  for  working  pressures 
of  over  one  hundred  and  seventy-five  (175)  pounds  gage 
or  when  it  is  necessary  to  place  a  fusible  plug  in  a  tube; 
in  which  cases  the  least  diameter  of  fusible  metal  shall 
not  be  less  than  three-eighths  (f)  inch. 

3.  The  location  of  fusible  plugs  shall  be  as  follows: 

(a)  In  Horizontal  Return-tubular  Boilers  —  In  the 
back  head,  not  less  than  two  (2)  inches  above  the  upper 
row  of  tubes,  and  projecting  through  the  sheet  not 
less  than  one  (i)  inch. 

(b)  In  Horizontal  Flue  Boilers —  In  the  back  head, 
on  a  line  with  the  highest  part  of  the  boiler  exposed 
to  the  products  of  combustion,  and  projecting  through 
the  sheet  not  less  than  one  (i)  inch. 

(c)  In  Locomotive  Type  or  Star  Water-tube  Boilers 
-  In  the  highest  part  of  the  crown  sheet,  and  pro- 
jecting through  the  sheet  not  less  than  one  (i)  inch. 

(d)  In  Vertical   Fire-tube   Boilers  —  In  an  outside 
tube,  placed  not  less  than  one-third  (J)  the  length  of 
the  tube  above  the  lower  tube-sheet. 

(e)  In   Vertical   Submerged-tube    Boilers  —  In   the 
upper  tube-sheet. 


182  BOILERS 

(/)  In  Water-tube  Boilers,  Horizontal  Drums,  Bab- 
cock  &  Wilcox  Type  —  In  the  upper  drum,  not  less 
than  six  (6)  inches  above  the  bottom  of  the  drum 
and  over  the  first  pass  of  the  products  of  combustion, 
projecting  through  the  sheet  not  less  than  one  (i)  inch. 

(g)  In  Stirling  Boilers,  Standard  Type  —  In  the 
front  side  of  the  middle  drum,  not  less  than  six  (6) 
inches  above  the  bottom  of  the  drum,  and  projecting 
through  the  sheet  not  less  than  one  (i)  inch. 

(h)  In  Stirling  Boilers,  Superheated  Type  —  In  the 
front  drum,  not  less  than  six  (6)  inches  above  the 
bottom  of  the  drum,  and  exposed  to  the  products  of 
combustion,  projecting  through  the  sheet  not  less  than 
one  (i)  inch. 

(/)  In  Water-tube  Boilers,  Heine  Type  —  In  the 
front  course  of  the  drum,  not  less  than  six  (6)  inches 
from  the  bottom  of  the  drum,  and  projecting  through 
the  sheet  not  less  than  one  (i)  inch. 

(/)  In  Robb-Mumford  Boilers,  Standard  Type  — 
In  the  bottom  of  the  steam  and  water  drum,  twenty- 
four  (24)  inches  from  the  center  of  the  rear  neck,  and 
projecting  through  the  sheet  not  less  than  one  (i)  inch. 

(k)  In  Water-tube  Boilers,  Almy  Type  —  In  a  tube 
directly  exposed  to  the  products  of  combustion. 

(/)    In  Vertical  Boilers,  Climax  or  Hazelton  Type  - 
In  a  tube  or  center  drum  not  less  than  one-half  (J)  the 
hight  of  the  shell,  measuring  from  the  lowest  circum- 
ferential seam. 

(m)  In  Cahall  Vertical  Water-tube  Boilers— In 
the  inner  sheet  of  the  top  drum,  not  less  than  six  (6) 
inches  above  the  upper  tube-sheet. 


BOILER    RULES  183 

(n)  In  Scotch  Marine  Type  Boilers  —  In  combus- 
tion-chamber top,  and  projecting  through  the  sheet 
not  less  than  one  (i)  inch. 

(0)  In  Dry-back  Scotch  Type  Boilers  —  In  rear 
head,  not  less  than  two  (2)  inches  above  the  top  row 
of  tubes,  and  projecting  through  the  sheet  not  less 
than  one  (i)  inch. 

(p)  In  Economic  Type  Boilers  —  In  the  rear  head, 
above  the  upper  row  of  tubes. 

(q)  In  Cast-iron  Sectional  Heating  Boilers — In 
a  section  over  and  in  direct  contact  with  the  products 
of  combustion  in  the  primary  combustion  chamber. 

(r)  For  other  types  and  new  designs,  fusible  plugs 
shall  be  placed  at  the  lowest  permissible  water  level 
in  the  direct  path  of  the  products  of  combustion,  as 
near  the  primary  combustion  chamber  as  possible. 


XVIII 

MECHANICAL   TUBE   CLEANERS 

THE  Hartford  Inspection  and  Insurance  Company, 
in  a  recent  issue  of  The  Locomotive,  sounds  a  note  of 
alarm  anent  the  damage  which  may  be  inflicted  upon  a 
boiler  by  the  improper  use  of  mechanically  operated 
tube  cleaners.  Coming,  as  it  does,  from  so  high  an 
authority,  this  warning  has  produced  unnecessary 
alarm  among  the  present  or  prospective  users  of  such 
devices,  and  the  statement  that  the  dangers  pointed  out 
are  incident  to  them  when  improperly  handled,  and 
that  "many  of  them  give  very  good  results  when  used 
judiciously  and  intelligently,"  is  lost  sight  of  in  the 
light  of  the  stated  fact  that  injury  has  been  produced 
by  their  use. 

The  first  instance  pointed  out  is  one  in  which  by  the 
use  of  a  cleaner  removing  external  scale  by  rapidly 
rapping  the  internal  surfaces  of  the  tubes  the  latter 
were  stretched  to  an  elliptical  section  to  such  an  extent 
that  several  of  them  collapsed  when  subjected  to  a 
pressure  of  ninety  pounds.  With  any  of  the  cleaners 
as  now  built  by  experienced  and  reputable  makers 
such  a  result  could  be  produced  only  by  the  grossest 
misuse  of  the  tool  and  the  most  flagrant  neglect  of  the 
directions  which  are  furnished  with  it.  Tests  made 

184 


MECHANICAL  TUBE   CLEANERS  185 

by  Professor  Kavanaugh,  of  the  University  of  Minne- 
sota, with  a  3J-inch  cleaner  prove  the  energy  of  the 
blow  when  operating  under  a  pressure  of  90  pounds 
to  be  .106  of  a  foot-pound  and  the  number  of  blows 
per  minute  4,560.  Only  slight  local  distortion  was 
produced  by  allowing  the  hammer  to  operate  continu- 
ously in  one  spot. 

It  appears,  therefore,  that  the  distortion  of  the  tubes 
in  the  case  mentioned  must  have  been  due  to  a  very 
unskilful  use  of  a  very  badly  designed  cleaner  rather 
than  to  the  fact  that  the  tubes  were  thinned  by  use 
but  still  serviceable.  The  same  remarks  will  apply  to 
the  cases  of  splitting  mentioned. 

Another  effect  is  the  lengthening  of  the  tubes  due 
to  the  peening  action,  causing  them  either  to  sag  or  to 
project  through  the  head.  This  action  might  follow  an 
unduly  protracted  application  of  even  a  good  cleaner, 
but  should  no.t  be  caused  by  such  application  as  is 
necessary  to  remove  ordinary  scale.  Such  elongation 
is  liable  to  crack  the  cast-iron  headers  of  water-tube 
boilers,  and  the  makers  of  at  least  one  of  the  cleaners 
of  this  type  discourage  for  this  reason  its  use  in  boilers 
with  headers  of  that  material.  Such  headers  are,  how- 
ever, dangerous  in  themselves  and  their  use  is  rapidly 
being  discontinued.  This  peening  effect  should  be 
present  in  the  mind  of  the  operator  of  the  cleaner,  and 
he  should  regulate  the  intensity  and  time  of  application 
of  the  blows  so  as  to  avoid  it,  and  watch  carefully  for 
it  at  the  tube  sheets. 

The  unequal  expansion  caused  by  discharging  the 
exhaust  from  steam-opera  ted  cleaners  through  the  tubes 


l86  BOILERS 

is  also  considered,  and  the  use  of  compressed  air  for 
running  the  cleaner,  when  available,  advised.  The 
makers  of  the  cleaners  are  alive  to  this  condition, 
recommend  the  use  of  air  in  preference  to  steam,  and 
recommend  also  that  the  boiler  be  cleaned  while  hot. 

The  conclusions  arrived  at  in  The  Locomotive  article 
are  as  follows: 

(i)  That  when  power-tube  cleaners  are  used  they 
should  be  kept  in  motion  so  that  they  cannot  strike  a 
succession  of  blows  against  any  one  part  of  the  tube; 

(2)  they  should  be  operated  by  a  pressure  not  exceeding 
20  pounds,  or,  at  the  most,  30  pounds  per  square  inch; 

(3)  steam  should  not  be  permitted  to  blow  through  the 
tubes  of  a  cold  boiler  for  a  sufficient  time  to  sensibly 
heat  the  tubes;    (4)  compressed  air  should  be  used  to 
operate  tube  cleaners  unless  the  motive  power  is  entirely 
external  to  the  tube;   (5)  in  any  case,  the  boiler  should 
be  carefully  watched  during  and  after  the  application 
of  a  power  cleaner,  especially  around  the  ends  of  the 
tubes  and  on  the  headers,  and  at  the  first  sign  of  dis- 
tress of  any  kind  the  use  of  the  cleaner  should  be 
promptly  discontinued;    (6)   lastly,  a   power  cleaner 
should  never  be  put  in  charge  of  any  attendant  save 
one  upon  whose  judgment  and  skill  the  owner  of  the 
boiler  can  implicitly  rely. 

These  conclusions  commend  themselves  even  to  the 
makers  of  the  devices  in  question,  with  the  exception 
that  they  claim  that  a  pressure  of  from  40  to  90  pounds 
is  better  than  the  lower  pressure  recommended  as  giving 
more  rapid  vibrations  and  of  less  amplitude,  and  deny 
that  the  heating  due  to  exhaust  steam  will  injure  a 


MECHANICAL  TUBE   CLEANERS  187 

sound  tube.  Signs  of  distress  may  be  evidences  of 
weakness  revealed  by  the  cleaner,  and  point  to  reforms 
or  repairs  rather  than  the  discontinuance  of  the  use 
of  the  cleaner.  The  strictures  apply  principally  to 
cleaners  operating  by  hammer  action  and  discharging 
steam  through  the  tube,  but  do  not  amount  to  a  con- 
demnation of  the  type,  the  successful  present  use  of 
over  5,000  machines  for  a  single  maker  evidencing  that 
injury  from  its  use  is  exceptional  and  avoidable  rather 
than  general  and  inherent. 


INDEX 

PAGE 

Air  bubbles 5 

Area  for  escape  of  steam    116 

to  be  braced  in  heads  of  horizontal  tubular  boilers,  finding  67 

Auxiliary  valve     115 

Average  unit  length 48 

Bagging  of  boilers 138 

Ball  of  safety  valve,  finding  distance  from  fulcrum 105 

of  safety  valve,  finding  weight 105 

safety  valve,  weight 119 

Beading  tube-end 160 

Blow  back     108 

-off  pipe,  care 148 

pipes,  faulty    140 

Blowing  off     148 

Boiler  appliances 123 

at  work,  watching i 

care  and  management 145 

compounds     : 138,  146 

rules 179 

Braces,  number    31 

Bracing,  amount    35 

heads  of  horizontal  tubular  boilers 67 

horizontal  return  tubular  boilers 30 

Bridgewall,  hight  and  form 137 

Bubbles,  air    5 

steam 5 

Bulge  on  fire-sheet 140 

Bursting  strength  of  boiler     17,    24,  29 

Butt-joint,  double-riveted  double-strapped    58 

189 


igo  INDEX 

PAGE 

Butt-joint,  single-riveted  double-strapped    57 

triple- riveted  double-strapped    61 

Calorific  value  of  various  woods 161 

Carle,  N.  A • 70 

Center  of  gravity,  distance  from  fulcrum    119' 

Chain  riveting 53 

Chimney  for  wood-burning  furnace 175 

Circle,  finding  area 80 

Circulation  in  U-tube    i 

Cleaning  boilers  138,  147 

tubes 137 

Combustion  chamber  in  wood-burning  furnace 170,  174 

chamber,  proper  depth 135 

Compressed  air  for  running  cleaner     186 

Cooling  boiler 148 

Cracks  in  settings    134 

Crushing  of  rivets  . .  .41,  44,  45,  47,  5°.  5*,  55,  56,  S8»  59.  60,  64,  71 

Diagonal  braces 31,  35 

Diagram,  calculating 72 

Diameter  of  rivets 70 

of  shell     70 

valve    112 

Disk  Y-valves 125 

Double  butt-strap,  efficiency 72 

lap,  efficiency    72 

-riveted  double-strapped  butt-joint 58 

lap-joint 49 

riveting 14,  23 

shearing 46 

Drilled  plate,  strength 43 

Dropped  forge  steel  flanges 128 

Dutch  oven 170,  172 

Factors  of  safety    29,  72,  1 80 


INDEX  191 

PAGE 

Feed  pipe,  point  of  discharge    143 

-water 147 

Feeding  boiler 142 

through  blow-off 142,  144 

wood-burning  furnace 174 

Flanges 1 28 

Force  acting  on  heads 17 

tensile 1 1 

Front  drum,  action  in 3,    4,    5 

Fuel  available 169 

Fulcrum 86 

Furnace  for  burning  wood 170 

Fusible  plugs    181 

Gage-glass  valves 127 

Graphical  determination  of  boiler  dimensions    70 

Grate  for  wood-burning  furnace 174 

Hartford  Inspection  and  Insurance  Co 184 

Heating  value  of  woods     164,  165 

Horizontal  tubular  boiler,  care    133 

Horse-power  of  boilers    1 20 

Huddling  chamber  of  safety  valve    106 

I-beams  for  setting  return  tubular  boilers    153,  154 

Jeter,  S.  F 40 

Johnston,  J.  A 161 

Joints,  proportion    50 

Kavanaugh,  Prof 185 

Kennett,  M 133 

Lap-joint,  double-riveted    49 

-joint,  single-riveted 48 

triple-riveted   51 


IQ2  INDEX 

PAGE 

Lap-riveted  joint  with  inside  strap     54 

joints,  single 72 

Leakage,  cold  air,  through  cracks  in  setting 134 

Lever,  length t  x  9 

of  safety  valve,  effect 95 

principle 84 

safety  valve 89 

valve,  amount  of  opening 115 

weight    .  .  .  .' 119 

Lift  of  valves 109,  in 

Lifting  force  of  safety  valve 103 

Locomotive,  The 184,  186 

Loss,  sources 134 

McConnaughy,  John  145 

Man-head  frames 1 29 

Mass.  Board  of  Boiler  Rules 179 

Model  boiler  i 

Moisture  content  of  woods 163 

Moment  of  a  weight  or  load 86 

of  lifting  force  of  safety  valve 103 

Moments,  measuring  for 98 

Mud-drum,  action  in 4,  5,  7 

-drum,  size    9 

Net  section    , 48 

section,  failure     50,  51,  58,  59,  60,  61,  64 

Nipples,  long 8,   10 

Oil    139 

Opening  of  lever  safety  valve,  amount 115 

Peening  action  of  cleaner 185 

Pitch , 13 

Plate  efficiency,  calculating    16 

strength 28 


INDEX  193 

PAGE 

Pop  safety  valve 100 

valve 1 16 

Position  of  weight  to  exert  pressure  on  stem  of  safety  valve.  .  .        93 

Pressure  against  head   30 

amount  boiler  will  stand 37 

at  which  valve  blows  off,  finding    104 

effect  in  lifting  a  valve 82 

of  changing 7>  9 

internal    17 

on  boilers,  maximum 179 

valve  to  lift  ball 91 

per  square  inch    75 

safe  working 29 

to  burst  a  shell 24,  28 

lift  valve  and  stem 119 

raise  lever   119 

raise  valve,  stem  and  lever 119 

Priming 9 

Projected  area    22,  25,  26 

Quadruple  butt-strap-riveted  joint 72 

-riveted  double-strapped  butt-joint 64 

Rear  drum,  action  in    4 

Reduction  of  pressure,  effect   9 

Refuse  for  fuel   169 

Return  tubular  boilers,  setting    150 

Rivet  efficiency 16 

holes 71 

resistance  to  crushing    41,    44 

Riveted  joints,  strength n,  28,  40,  41 

plate,  possible  modes  of  failure     41,  43 

Robbins,  C.  G 1 20 

Rupturing  plate 42,   43,    45 

Safety  valve    75,    1 23 


194  INDEX 

PAGE 

Safety  valve,  capacity   108 

care I48 

force  necessary  to  lift   79 

position     3,  9 

rules  103 

Scale,  avoiding 146 

Sediment .   4,  7,  9 

Segmental  area,  finding    34 

Segments  of  circles,  areas 37 

Separators 140 

Setting  return  tubular  boilers    150 

Sexton,  J.  E 156 

Shearing  of  rivets 13,  45,  48,  50,  51,  55,  56,  58,  59,  60,  61,  64 

strength  of  rivets 13,  41,  44,  46,  47,  70,  71,  180 

Sheet  strength 28 

Shell  formula    72 

Single  lap-riveted  joints   72 

-riveted  double-strapped  butt-joint 57 

lap-joint 48 

shearing 46 

Sizes  and  weights  of  columns  and  I-beams 154 

Sleeve  for  blow-off  pipe   141 

Smith,  C.  Hill i 

Solid  plate,  strength    '.  43 

Spacing  of  rivets    70,  71 

Spring-loaded  safety  valves   t 100 

Square  of  a  number,  finding 114 

Stack  area,  wood-burning  furnace   175 

Staggered  riveting   53 

Steam,  amount  escaping  through  opening 116 

bubbles    5 

gage   79,  127 

wet,  cause 6,  9 

withdrawing   9 

Steel  frames  and  nozzles 130 

lugs  supporting  boiler 131 


INDEX  195 

PAGE 

Stem,  distance  from  fulcrum  .............................  119 

Stop  valves  in  column  connection  .........................  126 

Strength,  ultimate  tensile  .................................  1  1 

Tensile  force  .......................................  1  1,  27,  28 

strength  ............................................  41 

of  cast  iron  and  forgings    ............................  129 

of  plate    ...........................................  70 

ultimate  ................  .  ..........................  1  1 

Test,  boiler  ............................................  3 

Testing  boiler  plate  .....................................  41 

machine  .............................................  41 

Thickness  of  plate  ......................................  70 

Through  braces    ......................................    31,   35 

Top  feed  .........................................  .  .....  142 

Triangle,  area  ..........................................  81 

Triple  butt-strap,  efficiency  ...............................  72 

lap,  efficiency    ........................................  72 

-riveted  double-strapped  butt-joint  ......................  61 

lap-joint     ..........................................  51 

Try-cocks    .............................................  127 

Tube  cleaners,  mechanical  ...............................  184 

Tubes,  cleaning    ........................................  137 

renewing  in  tubular  boiler  ..............................  156 

U-tube,  circulation  ......................................  i 

Ultimate  tensile  strength  .................................  1  1 

Unit  section  of  joint    ....................................  47 

United  States  Board  of  Supervising  Inspectors,  rules.  .  .  .36,  108,  no, 


Valve  area   .................................  108,  no,  112,  119 

auxiliary  .............................................      115 

diameter  .............................................      119 

lifting  ...............................................       82 

weight  with  stem  ......................................      119 


196  INDEX 

PACE 

Waste  pipe  for  safety  valve 1 24 

Water  column '. 125 

-tube  boilers  9 

Weight  of  valve  and  stem  of  safety  valve,  effect 95 

to  hold  pressure  on  valve 92 

Wet  steam 6>  9 

Wood  as  fuel  for  steam  boijers  161 

Working  pressure •  •  •  7° 

pressure,  safe   - 29 


UNIVERSITY   OF    CALIFORNIA 
LIBRARY 


This  is  the  date  on  which  this 
book  was  charged  out. 

OCT.  21911 


[30m-6,'ll] 


YB   10714 


196487 


